Depot tools git cl presubmit supports py2 and py3. However, presumbit
recipe only runs py2. This patch adds support for running py3 presubmit
checks too.

Bug: 1214829
Recipe-Nontrivial-Roll: build
Change-Id: I089460eaf65d4b6f1238eea13eb087fadb21cad5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2934371Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>