neutron is not starting up

[ulistack]

after having fought against many stoppers in opencontrail+devstack I now came to the point where neutron simply stops due to missing neutron plugin:
contrail is starting up.
In /home/stack/devstack/log/q-svc.log.2017-06-09-175011 you find:
ImportError: Plugin 'neutron_plugin_contrail.plugins.opencontrail.contrail_plugin_v3.NeutronPluginContrailCoreV3' not found.
one can reproduce the error by running:
/usr/local/bin/neutron-server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/opencontrail/ContrailPlugin.ini

stack@vm1:~/devstack$ cat /etc/neutron/plugins/opencontrail/ContrailPlugin.ini
[CONTRAIL]
api_server_ip = localhost
api_server_port = 8082
multi_tenancy = False

The Contrail API is working: ( tested with browser ), see :
stack@vm1:~/devstack$ netstat -an |grep 8082
tcp 0 0 0.0.0.0:8082 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:58420 127.0.0.1:8082 ESTABLISHED
tcp 0 0 127.0.0.1:8082 127.0.0.1:58416 ESTABLISHED
tcp 0 0 127.0.0.1:8082 127.0.0.1:58418 ESTABLISHED
tcp 0 0 127.0.0.1:58418 127.0.0.1:8082 ESTABLISHED
tcp 0 0 127.0.0.1:8082 127.0.0.1:57194 ESTABLISHED
tcp 0 0 127.0.0.1:58422 127.0.0.1:8082 ESTABLISHED
tcp 0 0 192.168.178.36:8082 192.168.178.36:40184 ESTABLISHED
tcp 0 0 127.0.0.1:8082 127.0.0.1:58422 ESTABLISHED
tcp 0 0 127.0.0.1:8082 127.0.0.1:57196 ESTABLISHED
tcp 0 0 127.0.0.1:57194 127.0.0.1:8082 ESTABLISHED
tcp 0 0 192.168.178.36:8082 192.168.178.36:40390 ESTABLISHED
tcp 0 0 127.0.0.1:60180 127.0.0.1:8082 TIME_WAIT
tcp 0 0 127.0.0.1:8082 127.0.0.1:58420 ESTABLISHED
tcp 0 0 127.0.0.1:60174 127.0.0.1:8082 TIME_WAIT
tcp 0 0 127.0.0.1:60186 127.0.0.1:8082 TIME_WAIT
tcp 0 0 127.0.0.1:57640 127.0.0.1:8082 ESTABLISHED
tcp 0 0 127.0.0.1:60168 127.0.0.1:8082 TIME_WAIT
tcp 0 0 127.0.0.1:57196 127.0.0.1:8082 ESTABLISHED
tcp 0 0 127.0.0.1:60042 127.0.0.1:8082 TIME_WAIT
tcp 0 0 127.0.0.1:8082 127.0.0.1:57640 ESTABLISHED
tcp 0 0 192.168.178.36:40184 192.168.178.36:8082 ESTABLISHED
tcp 0 0 192.168.178.36:40390 192.168.178.36:8082 ESTABLISHED
tcp 0 0 127.0.0.1:60190 127.0.0.1:8082 TIME_WAIT
tcp 0 0 127.0.0.1:58416 127.0.0.1:8082 ESTABLISHED

So what should I do ?

[ulistack]

Linux host ubuntu 14.04
Opencontrail master branch
devstack: stable/mitaka