Make client:auth more robust when login url cannot be reached

[tobiaslohr]

In some cases, when the login url of the authorization server (the Account Manager) cannot be reached, an exception is thrown and the command sfcc-ci client:auth does not gracefully print an error message but prints the stack trace to the console:

./node_modules/sfcc-ci/cli.js client:auth **** **** 

.../node_modules/sfcc-ci/lib/auth.js:235 } else if ( res.body && res.body['error_description']) { ^ TypeError: Cannot read property 'body' of undefined at Request._callback (.../node_modules/sfcc-ci/lib/auth.js:235:24) 
at self.callback (.../node_modules/request/request.js:185:22) 
at emitOne (events.js:96:13) 
at Request.emit (events.js:188:7) 
at Request.onRequestError (.../node_modules/request/request.js:881:8) 
at emitOne (events.js:96:13) 
at ClientRequest.emit (events.js:188:7) 
at TLSSocket.socketErrorListener (_http_client.js:314:9) 
at emitOne (events.js:96:13) 
at TLSSocket.emit (events.js:188:7)

Suggestion is the check on the response object being available and fallback to the err message passed to the callback function of the request module.