Netapp iscsi: allow snapshots with unspecified block range.

Snapshots were failing to create in all cases in the NetApp iscsi
driver. The clone lun function was never issuing the zapi call
because the block count was set to 0.

Closes-Bug: 1296881

Change-Id: Ic2bf67b57a566632103a3fa2ff032555f42a3961
Merge "Netapp iscsi: allow snapshots with unspecified block range."