Fix mock return settings in test_full_uuids_skip_port_id_lookup

Fix mock return settings in test_full_uuids_skip_port_id_lookup

In the test_full_uuids_skip_port_id_lookup test in test_security_group.py,
there are a couple of problems with how a mock return value is being set
for a database query.

The first problem is that in this line:
    fmock = sess_mock.query.return_value.outerjoin.return_value.filter
there is a missing '.return_value' missing between 'sess_mock' and 'query'.

The second problem is that in this line:
    fmock.return_value.all.return_value = []
the 'all.return_value' should not be used.

For reference, the query for which this mock return value is being set
is in the get_sg_ids_grouped_by_port() method in ML2's db.py:
        query = session.query(models_v2.Port,
                              sg_db.SecurityGroupPortBinding.security_group_id)
        query = query.outerjoin(sg_db.SecurityGroupPortBinding,
                                models_v2.Port.id == sg_binding_port)
        query = query.filter(or_(*or_criteria))

This patch fixes the problems mentioned above so that the query above
returns an empty list for the test_full_uuids_skip_port_id_lookup test.

Change-Id: I2cec2c27fcdc82557c91205d202a6ac79987e92a
Closes-Bug: 1444009