Creates a router if one doesn't exist

If it doesn't find a router by the name specified in router_name
in murano.conf, create a router with that name. Uses
external_network_id or external_network_name as the
external_gateway_info ID. Requires:
https://review.openstack.org/#/c/119800

Change-Id: If8b966a7d43eb2af485113de2a0708e554605725
Merge "Creates a router if one doesn't exist"