[WIP] Allow Kube proxy to watch for service/endpoint changes

Expose `GET /endpoints/<serviceName>`.  Allow watch on endpoints and with services with `fields=Name%3D<serviceName>`
I realize you didn't introduce this, but this "update" has a really bad use of AtomicUpdate. It will obliterate whatever is there, regardless of whether ```e``` was based on it or not. It's impossible to use this UpdateEndpoints function safely if there is a chance it can be called concurrently. Can you add a TODO?