This changes the script to query the command from mb.py then
call swarming trigger with -raw-cmd and -relative-cwd.

See http://crbug.com/chrome-operations/94

Bug: None
Change-Id: I1e11cd2e1314a4e96e1ee5a42b311f0c3cb5058b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2521240
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>