Should not allow assign floating IPs that are already assigned to another port

[Zhenyu Zheng]

While associate floating ip to instance, we did not check the floating IP is already assigned to
another port or not:
http://git.openstack.org/cgit/openstack/nova/tree/nova/network/neutronv2/api.py#n1684
It is understandable to allow re-assign to the same port, but we should not re-assgin
if it is already assigned to other ports.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/425077

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/425563

[Miguel Lavalle (minsel)]

This is not a bug, this is the expected behavior of the floating ip API in Neutron. Please look at this Tempest test case failure that was triggered by the proposed fix (https://review.openstack.org/#/c/425563/):

http://logs.openstack.org/63/425563/1/check/gate-tempest-dsvm-neutron-linuxbridge-ubuntu-xenial/4601f1d/console.html#_2017-01-26_08_51_05_811634

The source of this test is the following:

https://github.com/openstack/tempest/blob/master/tempest/api/network/test_floating_ips.py#L65

We are clearly saying in this test case's code that we allow to change a floating ip association without disassociating if before

[Miguel Lavalle (minsel)]

This is not a bug either in Nova. Please take a look at this Tempest API test:

https://github.com/openstack/tempest/blob/master/tempest/api/compute/floating_ips/test_floating_ips_actions.py#L109

and its failure as a consequence of the proposed Neutron fix:

https://github.com/openstack/tempest/blob/master/tempest/api/compute/floating_ips/test_floating_ips_actions.py#L109

[OpenStack Infra (hudson-openstack)]

Change abandoned by ZhaoBo (<email address hidden>) on branch: master
Review: https://review.openstack.org/425563

[OpenStack Infra (hudson-openstack)]

Change abandoned by Zhenyu Zheng (<email address hidden>) on branch: master
Review: https://review.openstack.org/425077