test_get_root_helper_child_pid_returns_first_child gate failure

http://logs.openstack.org/01/410501/5/check/gate-neutron-dsvm-functional-ubuntu-xenial/8a82bb0/testr_results.html.gz

ft1.1: neutron.tests.functional.agent.linux.test_utils.TestGetRootHelperChildPid.test_get_root_helper_child_pid_returns_first_child_StringException: Empty attachments:
  stderr
  stdout

pythonlogging:'': {{{
DEBUG [stevedore.extension] found extension EntryPoint.parse('zmq = oslo_messaging._drivers.impl_zmq:ZmqDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('amqp = oslo_messaging._drivers.impl_amqp1:ProtonDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('pika = oslo_messaging._drivers.impl_pika:PikaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('fake = oslo_messaging._drivers.impl_fake:FakeDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kombu = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kafka = oslo_messaging._drivers.impl_kafka:KafkaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('rabbit = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('zmq = oslo_messaging._drivers.impl_zmq:ZmqDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('amqp = oslo_messaging._drivers.impl_amqp1:ProtonDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('pika = oslo_messaging._drivers.impl_pika:PikaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('fake = oslo_messaging._drivers.impl_fake:FakeDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kombu = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kafka = oslo_messaging._drivers.impl_kafka:KafkaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('rabbit = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('zmq = oslo_messaging._drivers.impl_zmq:ZmqDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('amqp = oslo_messaging._drivers.impl_amqp1:ProtonDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('pika = oslo_messaging._drivers.impl_pika:PikaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('fake = oslo_messaging._drivers.impl_fake:FakeDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kombu = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kafka = oslo_messaging._drivers.impl_kafka:KafkaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('rabbit = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('zmq = oslo_messaging._drivers.impl_zmq:ZmqDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('amqp = oslo_messaging._drivers.impl_amqp1:ProtonDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('pika = oslo_messaging._drivers.impl_pika:PikaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('fake = oslo_messaging._drivers.impl_fake:FakeDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kombu = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('kafka = oslo_messaging._drivers.impl_kafka:KafkaDriver')
   DEBUG [stevedore.extension] found extension EntryPoint.parse('rabbit = oslo_messaging._drivers.impl_rabbit:RabbitDriver')
   DEBUG [oslo_policy._cache_handler] Reloading cached file /opt/stack/new/neutron/neutron/tests/etc/policy.json
   DEBUG [oslo_policy.policy] Reloaded policy file: /opt/stack/new/neutron/neutron/tests/etc/policy.json
}}}

Traceback (most recent call last):
  File "neutron/tests/base.py", line 116, in func
    return f(self, *args, **kwargs)
  File "neutron/tests/functional/agent/linux/test_utils.py", line 81, in test_get_root_helper_child_pid_returns_first_child
    sleep=0.1)
  File "neutron/common/utils.py", line 736, in wait_until_true
    while not predicate():
  File "neutron/tests/functional/agent/linux/test_utils.py", line 67, in wait_for_sleep_is_spawned
    return 'sleep' == processes[-1]
IndexError: list index out of range