Create MinionController to sync minions from cloudprovider (pkg cloudprovider/controller).
Remove OnceAndForever util, create a Run() method on MinionController.
Use Forbidden valdiation error when no capability
Merge pull request #1715 from ddysher/cloud-minion

Add external loop to sync minions from cloudprovider.
Merge pull request #1791 from erictune/new_validation_err

Use Forbidden valdiation error when no capability