This adds artifact output to the test runner. We add a fake test
at the start of a test run that owns the artifacts.

Bug: angleproject:5236
Change-Id: Ice8001bf1f2aafbd8123fee76e0e7fcc3e5a8a0c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2657535
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>