WIP: Re-implementing kube-up in go

This is very much a WIP. Wanted to get comments before I get too far down any rabbit holes.

kube-up.go follows the structure of kube-up in util.sh pretty closely. My next step is to take the library stuff currently in kube_updown.go and fit it nicely into the cloudprovider abstraction.

This is done now (although the "down" and "push" subcommands aren't yet functional)