/etc/neutron/neutron.conf:

-service_plugins = router
+service_plugins = neutron.services.l3_router.l3_router_plugin.L3RouterPlugin

# neutron-db-manage --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugin.ini upgrade head
No handlers could be found for logger "neutron.common.legacy"
INFO  [alembic.migration] Context impl MySQLImpl.
INFO  [alembic.migration] Will assume non-transactional DDL.
INFO  [alembic.migration] Running upgrade None -> folsom
INFO  [alembic.migration] Running upgrade folsom -> 2c4af419145b
...
INFO  [alembic.migration] Running upgrade 1341ed32cc1e -> grizzly
INFO  [alembic.migration] Running upgrade grizzly -> f489cf14a79c
INFO  [alembic.migration] Running upgrade f489cf14a79c -> 176a85fc7d79
...
INFO  [alembic.migration] Running upgrade 49f5e553f61f -> 40b0aff0302e
INFO  [alembic.migration] Running upgrade 40b0aff0302e -> havana
INFO  [alembic.migration] Running upgrade havana -> e197124d4b9
...
INFO  [alembic.migration] Running upgrade 538732fa21e1 -> 5ac1c354a051
INFO  [alembic.migration] Running upgrade 5ac1c354a051 -> icehouse

mysql> show tables;
+------------------------------+
| Tables_in_neutron            |
+------------------------------+
| agents                       |
| alembic_version              |
| allowedaddresspairs          |
| arista_provisioned_nets      |
| arista_provisioned_tenants   |
| arista_provisioned_vms       |
| cisco_ml2_credentials        |
| cisco_ml2_nexusport_bindings |
| consistencyhashes            |
| dnsnameservers               |
| externalnetworks             |
| extradhcpopts                |
| floatingips                  |
| ipallocationpools            |
| ipallocations                |
| ipavailabilityranges         |
| ml2_brocadenetworks          |
| ml2_brocadeports             |
| ml2_flat_allocations         |
| ml2_gre_allocations          |
| ml2_gre_endpoints            |
| ml2_network_segments         |
| ml2_port_bindings            |
| ml2_vlan_allocations         |
| ml2_vxlan_allocations        |
| ml2_vxlan_endpoints          |
| networkdhcpagentbindings     |
| networks                     |
| ports                        |
| routerl3agentbindings        |
| routerroutes                 |
| routers                      |
| securitygroupportbindings    |
| securitygrouprules           |
| securitygroups               |
| servicedefinitions           |
| servicetypes                 |
| subnetroutes                 |
| subnets                      |
+------------------------------+
39 rows in set (0.00 sec)