ext_framebuffer_multisample: Add an option to run accuracy tests for all sample counts

This patch adds 64 new piglit tests to spec/ext_framebuffer_multisample
and exposes a bug in Mesa's MSAA blit path on Broadwell.

Most of these tests currently fails on broadwell.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
ext_framebuffer_multisample: Use glDrawArrays in place of glDrawElements

Patch fixes an issue about generating the reference images in accuracy
tests.
In my view this patch should not make any change in test output. But,
it fixes the failures in 'accuracy' tests when run with 'all_samples'
and {depth_draw, depth_resolve, stencil_draw, stencil_resolve}
options. Tests with 'color' option continued passing with no changes
in output on NVIDIA drivers.

Without this patch, above tests failed with similar output (missing
reference images) on both i965 and NVIDIA proprietary linux drivers
(331.38). That rules out the possibility of driver bug. I spent some
time debugging it but couldn't figure out what's wrong with using
GL_ELEMENT_ARRAY_BUFFER and glDrawElements in these tests.
Setting element array buffers in two places, first in ManifestDepth
/ ManifestStencil and than in DownsampleProg, is causing some
problem.

I don't want to spend more time debugging this. So, I would like to
go ahead with this patch, even though it doesn't explain the problem
with using glDrawElements. Please let me know if you don't agree or
if you've some explanation of the observed behavior.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
fix