Description of problem:
When I ran manila scenario tests, some tests failed due to ssh key authentication.
I noticed that tests with single instance pass, however, tests with more than
one instance (e.g. "test_read_write_two_vms" test) fail.
I figured out that there is a mismatch between both instance keys.    
I tried to use a single key for both instances and the test passed. 

Version-Release number of selected component (if applicable):
puppet-manila-12.5.1-1.el7ost.noarch
python2-manilaclient-1.21.2-1.el7ost.noarch
python2-manila-tests-tempest-0.3.0-1.el7ost.noarch

How reproducible:
100%

Steps to Reproduce:
1. python -m unittest manila_tempest_tests.tests.scenario.test_share_basic_ops.TestShareBasicOpsNFS.test_read_write_two_vms

Actual results:
Unable to login, password is requested

Expected results:
Login with ssh key succeeded

Additional info:

Traceback (most recent call last):
  File "manila_tempest_tests/tests/scenario/test_share_basic_ops.py", line 161, in test_read_write_two_vms
    remote_client_inst1 = self.init_remote_client(instance1)
  File "manila_tempest_tests/tests/scenario/manager_share.py", line 169, in init_remote_client
        remote_client.exec_command("sudo umount %s" % target_dir)
    private_key=self.keypair['private_key'])
  File "manila_tempest_tests/tests/scenario/manager_share.py", line 263, in get_remote_client
    linux_client.validate_authentication()
  File "manila_tempest_tests/common/remote_client.py", line 51, in wrapper
    six.reraise(*original_exception)
  File "manila_tempest_tests/common/remote_client.py", line 32, in wrapper
    return function(self, *args, **kwargs)
  File "manila_tempest_tests/common/remote_client.py", line 92, in validate_authentication
    self.ssh_client.test_connection_auth()
  File "/home/stack/tempest-auto/.venv/lib/python2.7/site-packages/tempest/lib/common/ssh.py", line 207, in test_connection_auth
    connection = self._get_ssh_connection()
  File "/home/stack/tempest-auto/.venv/lib/python2.7/site-packages/tempest/lib/common/ssh.py", line 121, in _get_ssh_connection
    password=self.password)
tempest.lib.exceptions.SSHTimeout: Connection to the 10.0.0.218 via SSH timed out.
User: manila, Password: None