This adds support for running XTS from piglit.

This patch was original written by Eric Anholt, but I've cleaned it up
and reworked parts of it for upstreaming, and as a result I've attached
my name as the author so ``git bisect'' and ``git blame'' will send
angry mail my way instead of Eric's.

v2: - Don't break dmesg reporting
    - Use str.format consistently
    - populate profile after check for xtest symlink
v3: - rebase against master
    - fix spelling errors

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>