We have detected the same issue during the execution of a grenade job.  The conclusions are when the neutron-openvswitch-agent was starting

2016-11-07 19:37:42.028 28353 ERROR neutron.agent.linux.utils [req-76bce4d1-4005-4227-bfe4-c5d46ebe29b1 - -] Exit code: 255; Stdin: ; Stdout: ; Stderr: sysctl: cannot stat /proc/sys/net/bridge/bridge-nf-call-arptables: No such file or directory
...
2016-11-07 19:49:37.564 28353 ERROR ryu.lib.hub [req-76bce4d1-4005-4227-bfe4-c5d46ebe29b1 - -] hub: uncaught exception: Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/ryu/lib/hub.py", line 54, in _launch
    return func(*args, **kwargs)
  File "/opt/stack/old/neutron/neutron/plugins/ml2/drivers/openvswitch/agent/openflow/native/ovs_ryuapp.py", line 37, in agent_main_wrapper
    ovs_agent.main(bridge_classes)
  File "/opt/stack/old/neutron/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py", line 2175, in main
    agent.daemon_loop()
  File "/usr/local/lib/python2.7/dist-packages/osprofiler/profiler.py", line 154, in wrapper
    return f(*args, **kwargs)
  File "/opt/stack/old/neutron/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py", line 2096, in daemon_loop
    self.rpc_loop(polling_manager=pm)
  File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/opt/stack/old/neutron/neutron/agent/linux/polling.py", line 42, in get_polling_manager
    pm.stop()
  File "/opt/stack/old/neutron/neutron/agent/linux/polling.py", line 61, in stop
    self._monitor.stop()
  File "/opt/stack/old/neutron/neutron/agent/linux/async_process.py", line 129, in stop
    self._kill(kill_signal)
  File "/opt/stack/old/neutron/neutron/agent/linux/async_process.py", line 163, in _kill
    pid = self.pid
  File "/opt/stack/old/neutron/neutron/agent/linux/async_process.py", line 159, in pid
    run_as_root=self.run_as_root)
  File "/opt/stack/old/neutron/neutron/agent/linux/utils.py", line 240, in get_root_helper_child_pid
    pid = find_child_pids(pid)[0]
  File "/opt/stack/old/neutron/neutron/agent/linux/utils.py", line 181, in find_child_pids
    return []
  File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 220, in __exit__
    self.force_reraise()
  File "/usr/local/lib/python2.7/dist-packages/oslo_utils/excutils.py", line 196, in force_reraise
    six.reraise(self.type_, self.value, self.tb)
  File "/opt/stack/old/neutron/neutron/agent/linux/utils.py", line 173, in find_child_pids
    log_fail_as_error=False)
  File "/opt/stack/old/neutron/neutron/agent/linux/utils.py", line 144, in execute
    raise ProcessExecutionError(msg, returncode=returncode)
ProcessExecutionError: Exit code: -15; Stdin: ; Stdout: ; Stderr: Signal 15 (TERM) caught by ps (procps-ng version 3.3.10).
ps:display.c:66: please report this bug


2016-11-07 19:50:50.460 28353 ERROR neutron.plugins.ml2.drivers.openvswitch.agent.ovs_neutron_agent [-] Failed reporting state!

This seems to keep the address of the port and affects the target phase in grenade

2016-11-07 19:54:54.806 11875 ERROR ryu.lib.hub [-] hub: uncaught exception: Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/ryu/lib/hub.py", line 54, in _launch
    return func(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/ryu/controller/controller.py", line 97, in __call__
    self.ofp_ssl_listen_port)
  File "/usr/local/lib/python2.7/dist-packages/ryu/controller/controller.py", line 120, in server_loop
    datapath_connection_factory)
  File "/usr/local/lib/python2.7/dist-packages/ryu/lib/hub.py", line 117, in __init__
    self.server = eventlet.listen(listen_info)
  File "/usr/local/lib/python2.7/dist-packages/eventlet/convenience.py", line 43, in listen
    sock.bind(addr)
  File "/usr/lib/python2.7/socket.py", line 228, in meth
    return getattr(self._sock,name)(*args)
error: [Errno 98] Address already in use

2016-11-07 19:55:25.295 11875 ERROR neutron.plugins.ml2.drivers.openvswitch.agent.openflow.native.ofswitch [-] Switch connection timeout