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.
It might be worthwhile to add a comment that this image builds new certs when `docker build` is run and that is why the build is being done at install time instead of earlier.  We can look to find another way to generate/share certs later if need be.