Make neutron-server upgrade the database to head

Rather then upgrading to a specific version of OpenStack, just
upgrade to Head.  This works for both juno and kilo.

Change-Id: I6305218eabd7de0878e24c8fdae968ac6d612175
Partially-implements: blueprint port-kilo

docker/neutron/neutron-server/start.sh

@@ -93,6 +93,6 @@ if [[ ${MECHANISM_DRIVERS} =~ linuxbridge ]]; then
           "${NEUTRON_FLAT_NETWORK_NAME}:${NEUTRON_FLAT_NETWORK_INTERFACE}"
 fi
 
-su -s /bin/bash -c "neutron-db-manage --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/ml2_conf.ini upgrade juno" neutron
+su -s /bin/bash -c "neutron-db-manage --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/ml2_conf.ini upgrade head" neutron
 
 exec /usr/bin/neutron-server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/ml2_conf.ini