nova utils _boot_server function does not handle multiple networks

[Nir Magnezi]

Description of problem:
=======================
nova.utils._boot_server attaches an instance nic only to one network.
that prevents scenarios from booting instances attached to multiple networks.
For example:
 - an instance with multiple IPv4 networks
 - an instance with both IPv4 and IPv6 networks

Relevant Code (snipped from rally.benchmark.scenarios.nova.utils._boot_server()):

            if nets:
                net_idx = divmod(
                    (self.context["iteration"]
                     % self.context["config"]["users"]["tenants"]),
                    len(nets))[1]
                kwargs["nics"] = [{"net-id": nets[net_idx]}]

        server = self.clients("nova").servers.create(
            server_name, image_id, flavor_id, **kwargs

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/154833

[OpenStack Infra (hudson-openstack)]

Change abandoned by Nir Magnezi (<email address hidden>) on branch: master
Review: https://review.openstack.org/154833