We can't yet upgrade to version 5.x since it's only py3 compatbile and
some builders still rely on running gsutil with py2.

R=gavinmak@google.com

Bug: 1184108
Change-Id: I002cc3625a2184ab42383b88a014c0631d1a33ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3508516Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>