Rackspace - Switch to CoreOS for standard cluster

The Rackspace setup for Kubernetes now leverages CoreOS instead of Ubuntu. We've dropped Salt completely for the cluster.

This doesn't include the updated release scripts so I've left those in the icebox for now.
Be aware that this will miss any etcd entries that existed before this service was started.

You could add an ExecStart that recursively listed the keys and created the routing entries, but this leaves a small window between that script and this watch (without adding support for --after-index which is a bit awkward in shell).  A far simpler alternative is to use this feature (once submitted): https://github.com/coreos/etcdctl/pull/110