Create a backgroud task to register static list of machines.

Fix #2181
For the minion already exists case, it's annoying because I don't have a precise error code.  I can only get an error message, is there any way to interpret it?   The Create method call translates and swallows a lot information.
https://github.com/GoogleCloudPlatform/kubernetes/blob/master/pkg/client/minions.go#L45

For recreate and remove unhealthy minion, I think that's a larger changes that we can have separate issue & PR to disscus?  Like creating node status #2315