rietveld: Make upload.py's GetRpcServer() take explicit params.
rietveld: Make upload.py's GetRpcServer() take explicit params.

This function does some work to detect dev_appserver that git-cl
needs; we get prompted for a username and password otherwise.
I have a separate change to git-cl to make it use this function
instead of constructing a server object directly.

Patch by Dan Erat <derat@chromium.org>

Review URL: http://codereview.chromium.org/1635002

ligthyear/quick-check,ligthyear/quick-check