Add git similarity option to upload.py
Add git similarity option to upload.py

This change is to help tweak the rename heuristic in git so the file history is
properly presented in Rietveld.

Author: 40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org
Review: https://codereview.appspot.com/6574057/

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra