1. Change names of Pod statuses (Waiting, Running, Terminated).
2. Store assigned host in etcd.
3. Change pod key to /registry/pods/<podid>. Container location remains
the same (/registry/hosts/<machine>/kublet).
Files that have RESTStorage implementations now end in "storage", and
files that have registries now end in "registry". I removed some
underscores in file names, since it seems to be go style not to have
them. I split minion_registry.go into two files.
We should consider splitting this package into two, to make more clear
the separation between the layers.
