High: nfsserver: Cleanup shared nfs dir mount

I am testing nfs-server failover using DRBD as the shared storage.  I noticed when trying to do a failover that the DRBD drive could not transition between master and slave on the two nodes because the nfsserver agent never unmounted the device from the /var/lib/nfs directory.

Apparently the way we parse the 'mount' output is either outdated or does not catch my scenario.  I've left the old method in and added another check that searches to see if the /var/lib/nfs directory is mounted to the same device as our shared directory.  This solves my situation.