Add git_bootstrap.py, which bootstraps git on Windows using CIPD
Add git_bootstrap.py, which bootstraps git on Windows using CIPD

It's backwards compatible with the logic in win_tools.bat
and is intended to eventually replace it.

BUG=635421, 629679

Review-Url: https://codereview.chromium.org/2254843004

CoherentLabs/depot_tools,primiano/depot_tools,CoherentLabs/depot_tools,primiano/depot_tools,primiano/depot_tools