This is a reland of edb6e8c5

Original change's description:
> Add python3 support to bot_update recipe module
>
> Bug: 1227140
> Change-Id: Id4938c966da54957f84f59d0aef0c68c381ad5f6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3016032
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> Commit-Queue: Gavin Mak <gavinmak@google.com>

Bug: 1227140
Change-Id: I2d35d29f87236ce10ecabca41712cf1c90de8136
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3022310Reviewed-by: Anthony Polito <apolito@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>