Ensure network interfaces are in requested order

_build_network_info_model was iterating current_neutron_ports
instead of port_ids which contains ports in their correctly requested
order. Because of this the requested nic order was no longer being
perserved. This patch fixes this and also changes the order of ports
in test_build_network_info_model() so this case is tested.

Change-Id: Ia9e71364bca6cbc24ebc1c234e6a5af14f51cd62
Closes-bug: #1300325
Merge "Ensure network interfaces are in requested order"
Merge commit 'refs/changes/38/84138/2' of git://gold.eng.hq.xensource.com/git/github/openstack/nova into tmpbranch