[Gate fix] Change policy for create_port/update_port:fixed_ips

This commit fixes the policies used by the tests:

  * test_create_port_fixed_ips
  * test_update_port_fixed_ips

To validate the following policy actions instead:

  * create_port:fixed_ips:ip_address
  * update_port:fixed_ips:ip_address

This change is necessary because Neutron recently added more specific
policy enforcement for these actions in:

  I1046f6b13e68b1e274cc8f62f5b30aa5f8d71cdc

Also renames the test names to convey the more specific policy
name.

Change-Id: If123e20b10614e8e31ecaecf74e4beda6b575e40
1 file changed