The local address of the local endpoint for the VPN should be an unused
address on the external GW network of the Tier1 router
(and not the GW address itself).
To make sure this IP will not be used for anything else, a neutron port is
created.
The port will be deleted once the router (or its gw) is deleted.
The ip will be used for all the vpn services & connection on this tier1 router.
Change-Id: If956fd08f5c9cfde5cba9326c18d1d489c47a505
d97a333d21