Do not order by foreign key or it will return multiple rows for the same
object
Fix validation of NFS paths

The code would fail if the order of the forms were inverse, e.g.

/mnt/tank/test (directory)
/mnt/tank (mountpoint)

We do not allow sharing of a mountpoint and a directory simultaneously.
Allow null group

Ticket:	#5333
Properly populate nfs paths for update