gitlab-ci: Run piglit tests with llvmpipe

gitlab-ci: Run piglit tests with llvmpipe

One job for the quick_gl profile, one for the glslparser & quick_shader
profiles (doing these together takes hardly any more time than
quick_shader alone).

v2:
* Don't break lava tests
v3:
* Remove piglit test artifacts paths:
* Exclude some quick_shader tests again:
  - Test whose result flips between pass/fail/skip
  - *@vs_in tests, as not the same one of these gets picked every time
v4:
* Do not list passing tests in .gitlab-ci/piglit/*.txt (Eric Anholt)
* Include the test number summary in .gitlab-ci/piglit/*.txt
* Completely disable generating any vs_in tests in the piglit build.
* Remove some more unneded files from the piglit build tree.
* Exclude quick_gl arb_gpu_shader5 tests; they were all skipped anyway,
  as llvmpipe doesn't support this extension yet, but occasionally they
  would spuriously fail instead.
v5:
* Set LD_LIBRARY_PATH, so we actually test the Mesa build from the
  pipeline...
* Verify that wflinfo reports the expected Mesa version
* Pass -noreset to Xvfb
v6:
* Don't use autoscale runners, run piglit with -j4 (Eric Anholt)

Reviewed-by: Eric Anholt <eric@anholt.net>