When a subnet is created from a subnet pool, now is possible to undefine
the gateway IP. The new subnet created will have this value assigned to
None.
$ openstack subnet create --subnet-pool shared-default-subnetpool-v4 \
--network net14 snet14 --gateway None --format value \
--column gateway_ip
None
Closes-Bug: #2112453
Change-Id: I3bdd260f0f6b0259ff15cfe16a111bfe93b40749
5cccd2112f