Comment 18 for bug 1509101

In Contrail, all the stuff (service instance, scheduling, virtual machines, virtual machine interfaces, network namespaces...) to implement neutron router gateway (SNAT) is not instantiate until the router have at least one interface on a private network.
As tempest tests only set the router gateway and the proposed patch above uses the first right VMI of the first SI's VM as neutron port for the router gateway, no port is returned and tests failed.