VOLTHA is not connecting to several controllers

It is detected that, when several controllers are configured in ofagent config in docker compose, ofagent is not connecting properly.

Checking logs it can be seen that ConnectionManager is not getting a list of 'server:port' values but a full string with the --controller parameter value:

20180925T144033.858 INFO connection_mgr._init_

{controller_endpoints: ['192.168.83.37:6653 192.168.83.38:6653 192.168.83.39:6653'], event: list-of-controllers, instance_id: compose_ofagent_1}

but it should be

20180925T144033.858 INFO connection_mgr._init_

{controller_endpoints: ['192.168.83.37:6653', '192.168.83.38:6653', '192.168.83.39:6653'], event: list-of-controllers, instance_id: compose_ofagent_1}

This has been detected in tests done with onos cluster of 3 instances.