network_controller: allow local_ip to be the ip address from a named interface

[fcharlier]

On some deployments the instances tunnels are using a dedicated network interface, not the admin interface, the test should be updated to allow using the ip address from this interface.

See: https://github.com/enovance/openstack-serverspec/blob/master/spec/tests/networkcontroller/networkcontroller_spec.rb#L13

[goldyfruit]

:+1: https://github.com/goldyfruit/openstack-serverspec/blob/master/spec/tests/networkcontroller/networkcontroller_spec.rb#L13

[goldyfruit]

@fcharlier @EmilienM This issue is not a problem anymore due to this commit, no ? https://github.com/enovance/openstack-serverspec/commit/6834dfb7614e00d88d5e43da2d385e95540db53d