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.
My thinking there (and I'm open to suggestions) is that users download a distribution that has matched versions for client tools, scripts and binaries.  They then deploy out of that.  If we add/move/change servers it'll be bad/broken if users use these scripts to launch newer stuff.