[Piglit] Add X Test Suite integration

[Dylan Baker]

This is based on work originally done by Eric (Patches 1 and 4
originally written by him) I have added some generic framework in
patches 2 and 3 that are needed to get everything working, and done
cleanup work on patch 4 to get it ready for upstreaming. Currently
everything is working the same between the original version and this
one.

There is one thing that I haven't been able to test yet, and that is if
XTS fails and produces an image, if that image is moved into
$results_dir/images and linked into the results correctly.

Eric and Keith: Could you test and make sure this works for you? And
could one of you also be so kind as to break a test so it produces an
image output and see if that works?