Add fake port group fields for rule
Add fake port group fields for rule

Rule accepts port group dst and src so that the integration work
can go on without getting API errors.  This is intentional as
this feature will be implemented soon.

Signed-off-by: Ryu Ishimoto <079ed83f2117612507014e8df63a80b706c7096b@midokura.com>

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