Prepare for external scheduler

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).
Add debugging info printing to etcd fake

And make tests pass again.
Use DesiredState rather than CurrentState for Host.
Merge pull request #557 from lavalamp/podLocation

Prepare for external scheduler