The test was previously either masking every three aspect (color, depth
and stencil) or none.  This was not exercising every clear path in the
Vulkan backend.

Bug: angleproject:3241
Change-Id: Ief4085ea302ec17bffe30b1f8510ae357fd01290
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1551523
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>