This adds a wrapper script for run-tests.py that continues support for
iterating over multiple modes and architectures.

This also fixes a bug of the auto-detect target in gyp.

Bug: chromium:772804
Change-Id: I61ff47b12e1925e010d822327a8aae8c402f435d
Reviewed-on: https://chromium-review.googlesource.com/730225
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48794}