Set nova_additional_cell as global_vars
Set nova_additional_cell as global_vars

I9a37d1faec73a81a28d8f89d86375fb15ee765c7 moved to use ansible
for all_nodes hieradata. This also removed to create the
SERVICE_cell_node_names in in net_ip_list_map.j2.yaml.
This change addes nova_additional_cell to the global_vars that
the all_nodes hieradata via ansible can write cell service
hostnames.

Change-Id: I58c635b0fd92fa5a437cd6abd7c954d9cad720c9

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates