Set correct ObjectRef for port group src and dst
Set correct ObjectRef for port group src and dst

Signed-off-by: Rossella Sblendido <bc14cf5c5a5c23c483db75cf2384cf75c0f28746@midokura.com>

midokura/python-midonetclient,midonet/python-midonetclient,midokura/python-midonetclient,midonet/python-midonetclient