Add yapf and yapf.bat with a vpython spec, so it can be used anywhere, e.g.
bots.

Change-Id: I363c0251ed766b2bb15a8c0f03615bc9a3ecb37a
Reviewed-on: https://chromium-review.googlesource.com/1107170
Commit-Queue: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>