git cl format --python currently breaks on windows
because FindExecutable('yapf') returns .../depot_tools/yapf
(a py file) instead of .../depot_tools/yapf.bat. Also
yapf.bat tries to run the yapf py file without vpython
which breaks the yapf dependency.

This CL fixes these two issues.


Bug:846432
Change-Id: I551a4c1e6367074fa76767851bd34feb2dcfb6a2
Reviewed-on: https://chromium-review.googlesource.com/c/1341236Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Aiden Benner <abenner@google.com>