Syserror should contain the error message when process exits with error

[rgardler-msft]

Currently when an exec doc causes an error there is nothing in syserror. Output contains the entire output of the run, including things that ran successfully. This would allow for more accurate automated testing and resolution.

Syserror should contain the essential information, for example:

az network vnet create --resource-group $RESOURCE_GROUP_NAME_ED372 \
    --name $VNET_NAME_ED372 \
    --address-prefix $VNET_ADDRESS_SPACE_ED372 \
    --location $REGION_ED372

Expected output does not match actual output.                                                                                                                                                             
Got:                                                                                                                                                                                                      
{                                                                                                                                                                                                         
  "newVNet": {                                                                                                                                                                                            
    "addressSpace": {                                                                                                                                                                                     
      "addressPrefixes": [                                                                                                                                                                                
        "10.1.0.0/16"                                                                                                                                                                                     
      ]                                                                                                                                                                                                   
    },                                                                                                                                                                                                    
    "enableDdosProtection": false,                                                                                                                                                                        
    "etag": "W/\"f2d5e05d-7ebb-4d47-8f4b-5f3366d679bf\"",                                                                                                                                                 
    "id": "/subscriptions/f7a60fca-9977-4899-b907-005a076adbb6/resourceGroups/ExampleRG_edae6b/providers/Microsoft.Network/virtualNetworks/ExampleVNet_edae6b",                                           
    "location": "eastus",                                                                                                                                                                                 
    "name": "ExampleVNet_edae6b",                                                                                                                                                                         
    "privateEndpointVNetPolicies": "Disabled",                                                                                                                                                            
    "provisioningState": "Succeeded",                                                                                                                                                                     
    "resourceGroup": "ExampleRG_edae6b",                                                                                                                                                                  
    "resourceGuid": "xxxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",                                                                                                                                               
    "subnets": [],                                                                                                                                                                                        
    "type": "Microsoft.Network/virtualNetworks",                                                                                                                                                          
    "virtualNetworkPeerings": []                                                                                                                                                                          
  }                                                                                                                                                                                                       
}                                                                                                                                                                                                         
                                                                                                                                                                                                          
Expected:                                                                                                                                                                                                 
{                                                                                                                                                                                                         
    "newVNet": {                                                                                                                                                                                          
        "id": "/subscriptions/xxxxx-xxxxx-xxxxx-xxxxx/resourceGroups/ExampleRG_abc123/providers/Microsoft.Network/virtualNetworks/ExampleVNet_abc123",                                                    
        "location": "eastus",                                                                                                                                                                             
        "name": "ExampleVNet_abc123",                                                                                                                                                                     
        "properties": {                                                                                                                                                                                   
            "addressSpace": {                                                                                                                                                                             
                "addressPrefixes": [                                                                                                                                                                      
                    "10.1.0.0/16"                                                                                                                                                                         
                ]                                                                                                                                                                                         
            },                                                                                                                                                                                            
            "provisioningState": "Succeeded"                                                                                                                                                              
        },                                                                                                                                                                                                
        "tags": null                                                                                                                                                                                      
    }                                                                                                                                                                                                     
}                                                                                                                                                                                                         
                                                                                                                                                                                                          
Expected Score:0.800000                                                                                                                                                                                   
Actual Score:0.641925