Test Utils: Get executable path from command line. This simplifies the process fork test and will allow the test to work on Fuchsia. Bug: angleproject:3161 Change-Id: I5bb5424c44957f2faef1970b3cbc5e52b8aff630 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3788297 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Auto-Submit: Jamie Madill <jmadill@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>