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.
I'm not sure -- I could see going either way.  No need to lock it down now though.

In any case, it might be worthwhile to create a mime-encoded cloud-init package vs. putting everything into a single yaml file.  That is how we could start using the stuff from #1831.