'Makes sure plug doesn\'t drop FORWARD by default.
Ensures bug 890195 doesn\'t reappear.'

@mock.patch.object(linux_net.iptables_manager.ipv4['filter'], 'add_rule')
@mock.patch.object(utils, 'execute')
def test_linux_bridge_driver_plug(self, mock_execute, mock_add_rule):

    def fake_execute(*args, **kwargs):
        return ('', '')
    def verify_add_rule(chain, rule):
        self.assertEqual('FORWARD', chain)
        self.assertIn('ACCEPT', rule)
    mock_execute.side_effect = fake_execute
    mock_add_rule.side_effect = verify_add_rule
    driver = linux_net.LinuxBridgeInterfaceDriver()
    driver.plug({'bridge': 'br100', 'bridge_interface': 'eth0', 'share_address': False}, 'fakemac')
    self.assertEqual(2, mock_add_rule.call_count)
