This will allow us to use trigger.py in a standalone checkout
to fire off swarming jobs.

Bug: angleproject:5114
Change-Id: I99302a4e8fdfc0f6d9996748a2d6c97dc5f03cde
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2442079
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>