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.
Can we not add these functions in any more places? I'm trying to get them all out. The issue is that they don't show a useful line number, so you can't always tell what broke in your test, and they don't reduce typing very much anyway. :(