scripts: Changed uses of "ctdb xpnn" to ctdb_get_pnn()

scripts: Changed uses of "ctdb xpnn" to ctdb_get_pnn()

"ctdb xpnn" does not work when sysctl net.ipv4.ip_nonlocal_bind=1,
since it determines the node by attempting to bind to each addres in
the nodes file.  The solution is to not use "ctdb xpnn".  After the
initial call, ctdb_get_pnn() will be more efficient that "ctdb xpnn".

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
(Imported from commit 09b5e4978ab1df09f47156147848a6bf099ea665)