This is a reland of 0faae1c8

Original change's description:
> Use py3 in gitiles recipe module
>
> Recipe-Nontrivial-Roll: build
> Recipe-Nontrivial-Roll: chrome_release
> Recipe-Nontrivial-Roll: chromiumos
> Bug: 1289280
> Change-Id: I182f0e7ad1da58c1c707edd15675f6d30c5faed8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3438327
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
> Commit-Queue: Gavin Mak <gavinmak@google.com>

Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: chrome_release
Recipe-Nontrivial-Roll: chromiumos
Bug: 1289280
Change-Id: I9ba63a7cd4fea99c2043fae546c63ef942c82802
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3445785Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>