Use downstream config module

Because some distros do not contain the midonet upstream plugin
code, always use the downstream module for config.

Change-Id: I98742513cbbcf7d8c6190864b462297efa1bfb0d
Fixes: MN-3003
Signed-off-by: Ryu Ishimoto <ryu@midokura.com>

midonet/neutron/agent/midonet_driver.py

@@ -19,9 +19,9 @@
 # @author: Tomoe Sugihara, Midokura Japan KK
 # @author: Ryu Ishimoto, Midokura Japan KK
 
+from midonet.neutron.common import config  # noqa
 from neutron.agent.linux import dhcp
 from neutron.openstack.common import log as logging
-from neutron.plugins.midonet.common import config  # noqa
 
 LOG = logging.getLogger(__name__)