Use lists for uevent processing

Use lists for uevent processing

We now have proper list definitions, so we might as well use them
for uevent processing. And we can clean up signalling, too;
the pthreads condition signalling is unreliable, as a condition
signal might be lost if we're in the middle of processing. So
we should rather check the queue status prior to wait for a
condition.
And we can introduce a pthread cleanup handler, as well.

Signed-off-by: Hannes Reinecke <hare@suse.de>