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.
@jbeda thanks for the update. I was wondering why there 2 functions to upload the tar files. We don't plan on cutting releases so I'll move the "upload tar" code to the util.sh scripts.