GCE: Handle a nil configuration file

[nicksardo]

Fixes #1112

[k8s-reviewable]

This change is 

[coveralls]

Coverage decreased (-0.06%) to 44.614% when pulling bc5881b on nicksardo:gce-nil-config into 1516493 on kubernetes:master.

[nikhiljindal]

Is it expected to work without config?
If not, we should return an error here?

[nicksardo]

It should "work" without config assuming defaults are sane enough for the user.

[nikhiljindal]

optional nit: Update the message to say "No config file provided. Continuing with default values".
Config file not provided is different than not using config file.

[nicksardo]

Done

[nikhiljindal]

Instead of redefining getConfigReader, you can just update the variable that it returns.

configReader := nil
getConfigReader := func() io.Reader { return configReader }
if config != nil {
 // Update configReader
}

[nicksardo]

Not quite that simple. If we went this route, configReader would need to be reset for each loop iteration.

for {
   if config != nil {
       configReader = bytes.NewReader(allConfig)
   }
...
...
}

[nikhiljindal]

aah, got it.
Sorry for missing it the first time

[nikhiljindal]

thx, lgtm with an optional log message update suggestion

[coveralls]

Coverage decreased (-0.06%) to 44.725% when pulling df65973 on nicksardo:gce-nil-config into 81a36b4 on kubernetes:master.

[coveralls]

Coverage decreased (-0.06%) to 44.725% when pulling df65973 on nicksardo:gce-nil-config into 81a36b4 on kubernetes:master.