Pxf cluster config validation

[djianwen-vmware]

• add structs PxfServiceGroup, PxfCluster, PxfHost, and PxfDeployment.
• add Validation() to PxfDeployment.
• all the validation rules can be found under config_rules.go as private functions.
• IsValidAddress() is public for testing purpose
  • this function contains a permissive regex to match FQDN, which means it will return error only if it's obviously an invalid format.
• add tests with 100% statement coverage for config.go and config_rules.go

Validation rules and its corresponding functions:

• [x] Attribute values should be valid for their intended types (numbers, booleans, etc): achieved by Golang int, bool, etc. Only need to handle them when parsing the config file.
• [x] Cluster::name MUST be unique: achieved by Golang map
• [x] Cluster::collocated MUST not be NULL: achieved by Golang bool
• [x] Cluster::collocated==true SHOULD NOT have a list of hosts, they WILL be ignored: pxfClusterIgnoreHostsWhenCollocated
• [x] Cluster::collocated==true SHOULD NOT have a Cluster::endpoint, it WILL be ignored: pxfClusterIgnoreEndpointWhenCollocated
• [x] Cluster::collocated==false AND Cluster::endpoint==NULL MUST have a non-empty list of hosts: pxfClusterEndpointOrHostsMustExistWhenExternal
• [x] Cluster::endpoint != NULL MUST have a value of a valid IPv4 or FQDN compliant syntax: pxfClusterValidEndpoint
• [x] Host::hostname MUST be unique (a single host must belong to only one cluster): pxfDeploymentHostnameUnique
• [x] Host::hostname MUST have a value with either IPv4 or FQDN compliant syntax: pxfHostValidHostname
• [x] ServiceGroup::name MUST NOT be null / empty: pxfServiceGroupNameNotEmpty
• [x] ServiceGroup::name MUST be unique across all Clusters: pxfDeploymentGroupNameUnique
• [x] ServiceGroup::ports MUST be a non-empty array with at least 1 element: pxfServiceGroupAtLeastOnePort
• [x] ServiceGroup::ports elements MUST be an integer value between 1-65535: pxfServiceGroupValidPorts
• [x] ServiceGroup::ports elements SHOULD be larger than 1023 and smaller than 32768 (between privileged and ephemeral ranges): pxfServiceGroupPortsWarning
• [x] There MUST be at least one Cluster: pxfDeploymentAtLeastOneCluster
• [x] There MUST be no more than one Cluster::collocated==true: pxfDeploymentNoMoreThanOneCollocated
• [x] There MUST be at least one ServiceGroup per Cluster: pxfClusterAtLeastOneServiceGroup