[Piglit] RFC enhance dmesg handling in piglit

[Dylan Baker]

This series cleans up the dmesg handlingin piglit by implementing a
module with two classes, one for reading dmesg, and the other that acts
as a dummy class on non-posix systems, this allows dmesg to just always
be turned on all the time.

Secondly this new dmesg class has the ability to filter dmesg entries,
searching for specific regular expressions and classifying them as
either 'warns' or 'fails'.

Currently the filtering is fairly simply, and I expect to have at least
one more iteration of these patches with more enries for dmesg. It
curretly as an example marks any test the segfaults as a 'warn', and
searches for some entries emmitted by the i915 driver and marks them
'fail'.