With this change, stderr is also output when a test fails, including
logs such as those originating from UNIMPLEMENTED().

Bug: angleproject:6077
Change-Id: Ice1e1f9aff26acfb630aef99865503643f0a9658
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2976184
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>