Also replace mox with mock and move the test script to a different file.
Bug: 984182
Change-Id: I9005a523c2abd82c38a7c61501c7cbfd4201a5b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1745412
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>