[Piglit] piglit tests for EGL_KHR_create_context

[Matt Turner]

This series adds nine tests for EGL_KHR_create_context. It's based on
the GLX_ARB_create_context tests but with some differences.

These GLX_ARB_create_context tests aren't applicable:
 - Verify rejection of forward-compatible flag w/pre-3.0
 - Verify that invalid render types are rejected
 - Verify that color-index rendering is rejected with OpenGL 3.0

I don't have an implementation of EGL_KHR_create_context yet (Ian's
working on it) so the tests are written blind. I'm pretty sure there
are some problems with some of the attributes not being available under
ES (grep the spec for 'including OpenGL ES'.

Review and comments welcome.

Thanks,
Matt