Previously, dEQP would just use the first config returned which was
RGBA4 which is not very representitive of what our users would request.

BUG=angleproject:2337
BUG=angleproject:1095
BUG=angleproject:2222

Change-Id: I5c9defc7ce1feaa49407557b88d9bb6b98571771
Reviewed-on: https://chromium-review.googlesource.com/490726Reviewed-by: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>