Adds the depot tools path to be specified via the command line.
This will allow the bots to specify working directory locations.
Also adds quotes around the goma path in the gn args.

Bug: angleproject:5530
Change-Id: I1291a8cdf4e36e55786403b4d9a6ce8565093352
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2642894Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>