mongodb functional tests randomly failing

this is failing often enough that i notice it.

http://logs.openstack.org/55/219155/4/check/gate-ceilometer-dsvm-functional-mongodb/d9471d9/testr_results.html.gz

Traceback (most recent call last):
  File "ceilometer/tests/base.py", line 96, in skip_if_not_implemented
    return func(*args, **kwargs)
  File "ceilometer/tests/functional/api/v2/test_alarm_scenarios.py", line 48, in setUp
    super(TestAlarms, self).setUp()
  File "ceilometer/tests/functional/api/__init__.py", line 41, in setUp
    super(FunctionalTest, self).setUp()
  File "ceilometer/tests/db.py", line 218, in setUp
    self.useFixture(self.db_manager)
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/testtools/testcase.py", line 679, in useFixture
    reraise(*exc_info)
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/testtools/testcase.py", line 666, in useFixture
    fixture.setUp()
  File "ceilometer/tests/db.py", line 57, in setUp
    self.url, 'ceilometer.event.storage')
  File "ceilometer/storage/__init__.py", line 151, in get_connection
    return mgr.driver(url)
  File "ceilometer/event/storage/impl_mongodb.py", line 41, in __init__
    if self.conn.server_info()['versionArray'] < [2, 4]:
  File "ceilometer/storage/mongo/utils.py", line 415, in closure
    return call(*args, **kwargs)
  File "ceilometer/storage/mongo/utils.py", line 437, in __call__
    return self.method(*args, **kwargs)
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/pymongo/mongo_client.py", line 898, in server_info
    read_preference=ReadPreference.PRIMARY)
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/pymongo/database.py", line 451, in command
    with client._socket_for_reads(read_preference) as (sock_info, slave_ok):
  File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/pymongo/mongo_client.py", line 699, in _socket_for_reads
    with self._get_socket(read_preference) as sock_info:
  File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/pymongo/mongo_client.py", line 663, in _get_socket
    server = self._get_topology().select_server(selector)
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/pymongo/topology.py", line 121, in select_server
    address))
  File "/opt/stack/new/ceilometer/.tox/functional/local/lib/python2.7/site-packages/pymongo/topology.py", line 97, in select_servers
    self._error_message(selector))
pymongo.errors.ServerSelectionTimeoutError: connection closed