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.

The biggest change in this patch is that the --dmesg option is removed.
This is possible since the dmesg module implements a dummy class for
non-posix systems.

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>
gleantest.py: Use new dmesg class

This allows glean to use the dmesg class to check dmesg.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
es3conform.tests: Check dmesg

This allows es3conform to use the dmesg class.
NOTE: can someone confirm that this works?
igt.tests: make use of dmesg

This patch allows the igt integrated tests to use the new dmesg
implementation.

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