Periodically shows message while waiting for completion of REST operations

So that users understand what is happening.
It depends on which of glog.Infof and os.Stderr you prefer in the comment above.

If we keep using os.Stderr, since it is a UI for human end users, it should be kept separated from api client library.
Or it might be considerable to add something like

  // DoWaitFunc begins the request.  It calls waiter with the request and an operation ID when the request doesn't immediately complete, and waiter returns a new request to poll the status of the operation.
  func (r *Request) DoWaitFunc(waiter func (r *Request, op string) *Request) { ... }

If we use glog.Infof, I agree that it would be much simpler to just add glog.Infof into Request.Do.