GL RAII classes can't be used as test class members since the GL
objects need to be deleted before the test class TearDown is called.

BUG=angleproject:2765
TEST=angle_end2end_tests

Change-Id: If19d33bd044c9e74e46f35183e8ca1bc6a96d6cf
Reviewed-on: https://chromium-review.googlesource.com/1179159Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>