Request RGBA8 configs by default for gtest dEQP. 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/490726 Reviewed-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>