Track the temporary wakerefs used within the selftests so that leaks are
clear.

v2: Add a couple of coarse annotations for mock selftests as we now
loudly warn about the errors.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190114142129.24398-14-chris@chris-wilson.co.uk