tempest.api.network.test_floating_ips.FloatingIPTestJSON.
test_create_floating_ip_specifying_a_fixed_ip_address
fails to create floating ip as follows.

an external network with an ipv4 subnet + an ipv6 subnet is created.
Then, it tries to create floating ip. ODL returns bad request to neutron.

When creating/updating floating ip and attaching interface to router
subnets needs to exist.
The check is done by the number of subnets != 1.
But it should be done the number of ipv4 subnet == 0.

> Traceback (most recent call last):
> File "tempest/api/network/test_floating_ips.py", line 181, in test_create_floating_ip_specifying_a_fixed_ip_address
> fixed_ip_address=self.ports[1]['fixed_ips'][0]['ip_address'])
> File "tempest/services/network/json/network_client.py", line 188, in create_floatingip
> return self._create_resource(uri, post_data)
> File "tempest/services/network/json/network_client.py", line 109, in _create_resource
> resp, body = self.post(req_uri, req_post_data)
> File "/opt/stack/tempest/.venv/local/lib/python2.7/site-packages/tempest_lib/common/rest_client.py", line 256, in post
> return self.request('POST', url, extra_headers, headers, body)
> File "/opt/stack/tempest/.venv/local/lib/python2.7/site-packages/tempest_lib/common/rest_client.py", line 636, in request
> resp, resp_body)
> File "/opt/stack/tempest/.venv/local/lib/python2.7/site-packages/tempest_lib/common/rest_client.py", line 747, in _error_checker
> raise exceptions.ServerFault(resp_body, message=message)
> tempest_lib.exceptions.ServerFault: Got server fault
> Details: Request Failed: internal server error while processing your request.