The contextVk color mask needed to be updated when we
were syncing the state of the framebufferVk to make sure
the right mask gets applied in the test described in
ClearTest.cpp

Bug: angleproject:2685
Bug: angleproject:2597
Change-Id: I575028aad4cd495bf4ec1484cc870940dcde92d5
Reviewed-on: https://chromium-review.googlesource.com/1112038
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>