This is a reland of commit c0af61c8

Original change's description:
> Update gsutil to use gsutil version 5.6, python3
>
> R=gavinmak@google.com
>
> Bug: 1184108
> Change-Id: I933c07132006b731a97153080ebe86ed756fbdb2
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3497998
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

Bug: 1184108
Change-Id: I72c5b967f52e8b4531c238b20444596c549a5726
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3502172Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>