Fix IPv6 Network Deletion
Fix IPv6 Network Deletion

When an IPv6 network is deleted from the Infoblox grid, the ipam driver
checks whether more than one subnet exists in the network view.
However this check is done only on IPv4 network.
Added IPv6 network check.

Change-Id: I4fceacfb326f36002297a90525997a3104f7056d

openstack/networking-infoblox,openstack/networking-infoblox