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.
Cool -- I'll keep this in mind as we 'docker-ify' the rest of our server components and may steal/copy/ask you to merge this into main k8s.