Interestingly some ssh attempts fail with authentication failed:
    2020-02-04 06:53:40,627 101417 INFO     [paramiko.transport] Connected (version 2.0, client dropbear_2015.67)
    2020-02-04 06:53:40,937 101417 INFO     [paramiko.transport] Authentication (publickey) failed.
    2020-02-04 06:53:41,065 101417 ERROR    [tempest.lib.common.ssh] Failed to establish authenticated ssh connection to cirros@192.168.24.107 after 23 attempts
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh Traceback (most recent call last):
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh   File "/usr/lib/python2.7/site-packages/tempest/lib/common/ssh.py", line 107, in _get_ssh_connection
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh     sock=proxy_chan)
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh   File "/usr/lib/python2.7/site-packages/paramiko/client.py", line 437, in connect
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh     passphrase,
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh   File "/usr/lib/python2.7/site-packages/paramiko/client.py", line 749, in _auth
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh     raise saved_exception
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh AuthenticationException: Authentication failed.
    2020-02-04 06:53:41.065 101417 ERROR tempest.lib.common.ssh 


and others with ssh timeout:
    2020-02-04 06:53:42,797 101417 ERROR    [tempest.scenario.manager] Public network connectivity check failed. Reason: after re-associate floating ip
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager Traceback (most recent call last):
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/scenario/manager.py", line 729, in check_vm_connectivity
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     server=server)
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/scenario/manager.py", line 501, in get_remote_client
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     linux_client.validate_authentication()
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/lib/common/utils/linux/remote_client.py", line 60, in wrapper
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     six.reraise(*original_exception)
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/lib/common/utils/linux/remote_client.py", line 33, in wrapper
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     return function(self, *args, **kwargs)
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/lib/common/utils/linux/remote_client.py", line 116, in validate_authentication
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     self.ssh_client.test_connection_auth()
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/lib/common/ssh.py", line 207, in test_connection_auth
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     connection = self._get_ssh_connection()
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager   File "/usr/lib/python2.7/site-packages/tempest/lib/common/ssh.py", line 121, in _get_ssh_connection
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager     password=self.password)
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager SSHTimeout: Connection to the 192.168.24.107 via SSH timed out.
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager User: cirros, Password: None
    2020-02-04 06:53:42.797 101417 ERROR tempest.scenario.manager