This contains tests for framebuffer completeness when layers of
multisample array textures are attached.

Simple clearing of a layer of a multisample color texture array and
blitting the result to a non-multisampled texture is also covered.

BUG=angleproject:2775
TEST=angle_end2end_tests

Change-Id: Idf383cab69587dbd8157ab9a2b7c47e5a90b3cf7
Reviewed-on: https://chromium-review.googlesource.com/1190184Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>