Refactor test_ipam functional testing module
Refactor test_ipam functional testing module

Use existing testing ifrastructure to better integrate with the rest of
Neutron tests. This change allows test_ipam module to work with future
db engine facade changes.

Change-Id: I6c95cce56f36dd0c97f727c337ef6af04bc13a40
Related-Bug: 1520719

sebrandon1/neutron,cloudbase/neutron,mahak/neutron,igor-toga/local-snat,noironetworks/neutron,noironetworks/neutron,openstack/neutron,cloudbase/neutron,mahak/neutron,openstack/neutron,openstack/neutron,huntxu/neutron,eayunstack/neutron,eayunstack/neutron,igor-toga/local-snat,huntxu/neutron,sebrandon1/neutron,mahak/neutron