Neutron Allowed Address Pair API test

Adds a script to test the Neutron API extension for Allowed Address Pair.

Also adds to the xml ReST clent for Neutron the plurals definition for allowed
address pairs

Change-Id: I1dd1e299f4436f5a613351f612cb078e630c7026
Merge "Neutron Allowed Address Pair API test"
Merge branch 'master' of https://github.com/openstack/tempest