udevd: export event queue and event state

udevd: export event queue and event state

All pending and running events can be found as symlinks to the actual
device in /dev/.udev/queue/ now. This way we can lookup if specific events
are still in the queue, before doing actions which require events to have
finished.

All failed event processes can be found in /dev/.udev/failed/. This makes
it possible to retry a failed event process at a later time in the boot
process.

Signed-off-by: Kay Sievers <kay.sievers@suse.de>