Use config sources for Kubelet, switch to podFullName

As discussed in #297 and also a side discussion about abstracting the Kubelet from being directly dependent on etcd, start refactoring config service to decouple sources of config from sync loop and switch from Manifest.ID -> Pod Full Name in the Kubelet.

Simplifies the Kubelet Run() step by requiring configuration to be defined up front, and an update channel passed into the Kubelet.
A question rather than a statement.  Does it make life cleaner or messier to start the goroutine here, or to let cmd/kubelet call "go etcd.Run()"?  Most of the other kubelet goroutines start there, so maybe the consistency is worthwhile.