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's mostly to regenerate the self-signed certificate at build time and store that in the image.

The other piece is as you said, just for the http auth. I don't think ENVs are the best option since you would need some way to turn those variables into an htpasswd file and restart nginx. Doable, which way is less dirty?

Volume mounts would be interesting too and I didn't really think about those. I'm a fan of keeping everything contained in the image if possible but I can see that working too.