vdev_id: extension for new scsi topology

On systems with SCSI rather than SAS disk topology, this change enables
the vdev_id script to match against the block device path, and therefore
create a vdev alias in /dev/disk/by-vdev.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Simon Guest <simon.guest@tesujimath.org>
Closes #6592