This module reworks the dmesg testing to be much more robust, largely by
taking advantage of the mock module. This allows us test test dmesg
without actually calling dmesg, which eliminates the need for root
privileges, and allowing all tests to run on all platforms.

These tests also don't probe at the internal bits of the class, instead
they probe at the public API.

This significantly simplifies the tests, increases coverage, and
improves the quality of the tests in many cases, while making some of
the tests less fragile but less specific in other cases.

v2: - add tests for dmesg wrapping. Tests for this functionality where
      present in the replaced implementation.
    - remove '--attr=\!privileged' from tox.ini. There are now no
      privileged tests, so no need to exclude them

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>