framework/dmesg: Adds a new module for dmesg

This class implements a class for reading dmesg, including a dummy class
for running on non-posix systems. It works as a class, and is cleaner
than the current implementation.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
dmesg: Use the dmesg class instead of the dmesg functions

This requires some minor changes, since the dmesg class returns either
None or [] (which are both falsy instances) instead of '' when not
giving a dmesg warning.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
dmesg: setup dmesg to be able to mark a test warn or fail

This gives the dmesg class lists of statuses that will make a test a
warn or a fail, it includes a few basic checks, namely i915 errors and
that tests have not segfaulted.

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