[Piglit] Last set of all.py rework

[Dylan Baker]

This is the last set of patches for my all.py rework. The basic changes
can be boiled down to:

1) Autodiscover asmparser tests like glslparser and shader tests.
2) Use a context manager to add tests. This is clean, simple and gives
   some variable isolation
3) Flip run_concurrent from False by default to True by default, and
   flip the arguments in all.py to match. This also changes CL so that
   the PiglitCLTest class tests for concurrency safety and picks the
   right default.

This is available at my github:
https://github.com/dcbaker/piglit submit/flat-test-list-final