the revert mechanism for the Python bundle patch relies on the resitual
"python_bin_reldir.txt" file existing. Apparently "bot_update" purges
this file as part of its depot_tools checkout, breaking the revert
mechanism. Whitelist it so that this stops happening.

TBR=tandrii@chromium.org
BUG=chromium:741650
TEST=None

Change-Id: Id6b7c966b6fa3f5084be5e1906b3e10d38ab8b6c
Reviewed-on: https://chromium-review.googlesource.com/568530Reviewed-by: Daniel Jacques <dnj@chromium.org>
Commit-Queue: Daniel Jacques <dnj@chromium.org>