CLOUDSTACK-7331: Fixed issue in test_persistent_networks.py
CLOUDSTACK-7345 changed dd blocksize to 128k when using NFS.

Signed-off-by: Daan Hoogland <daan@onecht.net>
(cherry picked from commit 8b7130fa65a3ce010a54015b3350b94b56414462)
CLOUDSTACK-5663 : Added the NULL CIDR check to avoid NPE for createNetwork and listNetwork

Signed-off-by: Daan Hoogland <daan@onecht.net>