Bug 1852375

Description of problem:
Our unified job detect failure in neutron_tempest_plugin.scenario.test_port_forwardings.PortForwardingTestJSON.test_port_forwarding_to_2_servers

the error: 
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/test_port_forwardings.py", line 123, in test_port_forwarding_to_2_servers
    self._test_udp_port_forwarding(servers)
  File "/usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/test_port_forwardings.py", line 108, in _test_udp_port_forwarding
    server['id'])))
  File "/usr/lib/python3.6/site-packages/neutron_tempest_plugin/common/utils.py", line 77, in wait_until_true
    while not predicate():
  File "/usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/test_port_forwardings.py", line 105, in <lambda>
    lambda: _message_received(server, ssh_client, expected_msg),
  File "/usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/test_port_forwardings.py", line 94, in _message_received
    constants.PROTO_NAME_UDP)
  File "/usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/base.py", line 489, in nc_client
    self.assertEqual(0, result.exit_status)
  File "/usr/lib/python3.6/site-packages/testtools/testcase.py", line 411, in assertEqual
    self.assertThat(observed, matcher, message)
  File "/usr/lib/python3.6/site-packages/testtools/testcase.py", line 498, in assertThat
    raise mismatch_error
testtools.matchers._impl.MismatchError: 0 != 1


Ncat: Version 7.70 ( https://nmap.org/ncat )

 execute /usr/lib/python3.6/site-packages/neutron_tempest_plugin/common/shell.py:77
2020-06-30 04:20:34.819 673245 DEBUG neutron_tempest_plugin.common.shell [-] Executing command 'echo "knock knock" | nc -z -w 1 -u 10.0.0.212 1036' on local host (timeout=None)... execute_local_command /usr/lib/python3.6/site-packages/neutron_tempest_plugin/common/shell.py:127
testtools.matchers._impl.MismatchError: 0 != 1
> /usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/test_port_forwardings.py(124)test_port_forwarding_to_2_servers()
-> self._test_udp_port_forwarding(servers)
(Pdb) self._test_udp_port_forwarding(servers)
2020-06-30 04:20:40.102 673245 INFO tempest.lib.common.ssh [-] Creating ssh connection to '10.0.0.212:1026' as 'cirros' with public key authentication
2020-06-30 04:20:40.106 673245 INFO paramiko.transport [-] Connected (version 2.0, client dropbear_2015.67)
2020-06-30 04:20:40.176 673245 INFO paramiko.transport [-] Authentication (publickey) successful!
2020-06-30 04:20:40.177 673245 INFO tempest.lib.common.ssh [-] ssh connection to cirros.0.212 successfully created
2020-06-30 04:20:40.320 673245 DEBUG neutron_tempest_plugin.common.shell [-] Executing command 'ncat --version 2>&1' on local host (timeout=None)... execute_local_command /usr/lib/python3.6/site-packages/neutron_tempest_plugin/common/shell.py:127
2020-06-30 04:20:40.334 673245 DEBUG neutron_tempest_plugin.common.shell [-] Command 'ncat --version 2>&1' succeeded:
stderr:

stdout:
Ncat: Version 7.70 ( https://nmap.org/ncat )

 execute /usr/lib/python3.6/site-packages/neutron_tempest_plugin/common/shell.py:77
2020-06-30 04:20:40.335 673245 DEBUG neutron_tempest_plugin.common.shell [-] Executing command 'echo "knock knock" | nc -z -w 1 -u 10.0.0.212 1036' on local host (timeout=None)... execute_local_command /usr/lib/python3.6/site-packages/neutron_tempest_plugin/common/shell.py:127
*** testtools.matchers._impl.MismatchError: 0 != 1
(Pdb) n
--Return--
> /usr/lib/python3.6/site-packages/neutron_tempest_plugin/scenario/test_port_forwardings.py(124)test_port_forwarding_to_2_servers()->None
-> self._test_udp_port_forwarding(servers)
(Pdb) n
testtools.matchers._impl.MismatchError: 0 != 1
> /usr/lib/python3.6/site-packages/testtools/testcase.py(719)_run_test_method()
-> return self._get_test_method()()
Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
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Actual results:


Expected results:


Additional info: