[Intel-gfx] IGT conventions

[Jeff McGee]

There doesn't seem to be anything like the exit handlers for running when
a subtest exits. I need a failed subtest to be able to cleanup after
itself to avoid contaminating subsequent subtests. Have I missed something?
Perhaps this is not a problem when running subtests individually through
piglit?

I guess one simple approach is to wrap igt_assert with the cleanup
function, like the restore_assert that was originally used in pm_rps.

Jeff