The patch restructures the tests in MultiviewDrawTests.cpp, so that
all rendering tests can be instantiated for side-by-side and layered
framebuffers.

BUG=angleproject:2062
TEST=angle_end2end_tests

Change-Id: I2c32fd3bd57b6afd1eb8d6cedb2d1b88b9fd6525
Reviewed-on: https://chromium-review.googlesource.com/627918
Commit-Queue: Martin Radev <mradev@nvidia.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>