graphics tests: Bubble up errors from stderr.

Right now when external binaries are ran and fail due to a check this
may lead to a passing test. Try to catch this.

BUG=None.
TEST=Ran on nyan_big, observed graphics_SyncControlTest failing.

Change-Id: I1ea99d4bdf6539130ed964f2d2c55c8d0d7ee695
Reviewed-on: https://chromium-review.googlesource.com/220030
Commit-Queue: Ilja Friedel <ihf@chromium.org>
Tested-by: Ilja Friedel <ihf@chromium.org>
Reviewed-by: Haixia Shi <hshi@chromium.org>
6 files changed