Handle inability to login to Salesforce more cleanly

[metadaddy]

Currently, we just log the error and carry on, even though nothing will work. For example,

2014-04-21 22:49:32 [INFO] [STDOUT] Logging in to login.salesforce.com as [email protected]
2014-04-21 22:49:32 [INFO] [STDOUT] executing POST https://login.salesforce.com/services/oauth2/token
2014-04-21 22:49:33 [INFO] [STDOUT] ----------------------------------------
2014-04-21 22:49:33 [INFO] [STDOUT] error: invalid_grant
2014-04-21 22:49:33 [INFO] [STDOUT] error_description: authentication failure - Failed: API security token required
2014-04-21 22:49:33 [INFO] [STDOUT] ----------------------------------------

We should somehow show the error more visibly, then fail sooner.