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.
Is there a reason to build this again locally, rather than just have (you) publish a docker image directly?

Oh, is this just to get the kubernetes_auth user:pass inside the container?  Is there a reason we can't just pass those via regular docker environment variables (or volume mounts, if we want to avoid them appearing in environment/command lines)