We separate out the `create cluster` operation from the `update cluster`
operation. Now create cluster only creates the spec (unless you pass
--yes), and is only for new clusters.
`update cluster` works on new or existing clusters, and should be called
to apply changes.
`update` is not the best name, because it means something different in
kubectl, but I think it's a good start.
StateStore was highly orientated towards a VFS system; replace it with a
Registry abstraction that is more object based.
We also rationalize much of the CLI (cmd) command logic also.