core.Environment: squash pylint warnings

This adds Environment.options = None, so that pylint will stop
complaining. This doesn't change any functionality at all.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
Revert "summary.py: Treat subtests as groups"

This reverts commit e0d4bdbaa38a7441b0f38e115bd2daf3c6a05da3.
Revert "core.py: don't write subtests as full entries"

This reverts commit e8bfd585f0df4c9fb49080f19fb8c33a820733b2.
Check that uniform block link errors are detected when skipping stages.

In Mesa, as of commit f38ac41, uniform blocks are only validated
between adjacent shader stages.  That means that if a program contains
vertex, geometry, and fragment shader stages, and the vertex and
fragment shader stages refer to a uniform block that isn't referred to
by the geometry stage, then some linker checks may not be performed.

Most possible link errors get detected at a later stage of linking,
but I found one case that wasn't; this test exercises that case.