tests/igt.py: Minor changes

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
tests/oglconform.py: Set __all__

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
tests/all_cl.py: set __all__

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
Remove execfile from core

This completely kills execfile, but I'm not sure I'm happy with the
implementation.
core.py: Add helper to TestProfile reduce dependency checking boiler

This allows test profiles that need to check for specific dependencies
an easy interface for doing so. This allows the profile to remain
simple, and the code to remain in a single location.

updates oglconform, es3conform, and igt profiles to use this new code