This is a rather sizeable commit, I'm sorry for that. Basically there
was no clean way I could come up with to make the change from a single
python file to multiple xml files.

The reason we want this is to to avoid duplication amongst profiles (and
very long build times), by allowing a single profile to be included in
multiple other profiles. This means that the all profile is now composed
of the "glslparser", "shader", and "opengl" (everything in all that's
not glslparser, asmparser, or shader tests). Running `piglit run all
foo` still produces the same results. This also allows us to mix native
and non-native tests so that traditional targets like quick_cl still
work.

Tested-by: Rafael Antognolli <rafael.antognolli@intel.com>