kpartx: create correct symlinks for PATH_FAILED events

The kernel is sending out PATH_FAILED/PATH_REINSTATED events,
upon each of which we need to regenerate the existing symlinks.
However, for an all-paths-down scenario we cannot read from
the disk, so we cannot execute blkid or kpartx.
For these cases we need to import the existing data from the
udev database.

References: bnc#797799

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