This is a reland of commit 8edc960e

Original change's description:
> Update gsutil to use gsutil version 4.68
>
> 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/+/3508516
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

Bug: 1184108
Change-Id: I8f4b726c203ed12d415deeec249972fe855b59c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3514940Reviewed-by: Brian Ryner <bryner@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>