Fix neutron-agents start commands in OCF

W/o this fix, n-agents can not detach start command
and create a pidfile
The solution is to fix start command as appropriate

Closes-bug: #1389299

Change-Id: I46e1cf286622db0d64e9f17f72ed632e43906e05
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>