Comment 3 for bug 1577963

Next layer of the onion, nova made a recent change that broke the ability to reattach a port to a new instance.

The change that broke us: https://review.openstack.org/#/c/264017/
The bug I opened: https://launchpad.net/bugs/1602357
The proposed fix: https://review.openstack.org/#/c/341102/
A tempest test to catch this in the future: https://review.openstack.org/#/c/341191/