The undercloud needs the External network for the external VIP
address. It uses the _from_pool template creating a fake neutron
Other networks are not required, and should be removed to optimize
the number of heat resources and plan rendering.
NOTE: Skips validation of network_data_undercloud.yaml against
network_data.yaml, as is already done to openshift and routed
networks networks data examples.
Related Bug: #1809313