Comment 3 for bug 1570908

There were two reasons for this test to fail:
1. An issue with re-triggering new traversal as described in https://bugs.launchpad.net/heat/+bug/1625073
2. The restore_prev_resource in server_network_mixin has to care of a situation mentioned above bug, i.e. a replacement is created but it could never take off because the stack was rolled back. So the replacement resource exists in DB but there is no physical resource. I have updated the patch https://review.openstack.org/306490