Cannot specify ssh private key for tests

[Evgeny Sikachev]

ENVIRONMENT: master 06 apr 2016

STEPS TO REPRODUCE:
1. Create any cluster(with ssh-key from another host)
2. Get id of this cluster
3. Add existing_cluster to scenario for this cluster
4. Run scenario

EXPECTED RESULT:
Test passed

ACTUAL RESULT:
Captured pythonlogging:
~~~~~~~~~~~~~~~~~~~~~~~
    2016-04-06 10:22:35,737 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 1. Retry after 2 seco
nds.
    2016-04-06 10:22:38,589 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 2. Retry after 3 seco
nds.
    2016-04-06 10:22:42,297 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 3. Retry after 4 seco
nds.
    2016-04-06 10:22:47,022 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 4. Retry after 5 seco
nds.
    2016-04-06 10:22:52,730 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 5. Retry after 6 seco
nds.
    2016-04-06 10:22:59,507 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 6. Retry after 7 seco
nds.
    2016-04-06 10:23:07,360 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 7. Retry after 8 seco
nds.
    2016-04-06 10:23:16,122 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 8. Retry after 9 seco
nds.
    2016-04-06 10:23:25,831 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 9. Retry after 10 sec
onds.
    2016-04-06 10:23:36,810 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 10. Retry after 11 se
conds.
    2016-04-06 10:23:48,607 3988 WARNING [tempest_lib.common.ssh] Failed to establish authenticated ssh connection to ubuntu@172.18.79.196 (Authentication failed.). Number attempts: 11. Retry after 12 se
conds.
    2016-04-06 10:24:01,134 3988 ERROR [paramiko.transport] Exception: Error reading SSH protocol banner
    2016-04-06 10:24:01,154 3988 ERROR [paramiko.transport] Traceback (most recent call last):
    2016-04-06 10:24:01,155 3988 ERROR [paramiko.transport] File "/home/qa/sahara-tests/.tox/venv/local/lib/python2.7/site-packages/paramiko/transport.py", line 1710, in run
    2016-04-06 10:24:01,155 3988 ERROR [paramiko.transport] self._check_banner()
    2016-04-06 10:24:01,155 3988 ERROR [paramiko.transport] File "/home/qa/sahara-tests/.tox/venv/local/lib/python2.7/site-packages/paramiko/transport.py", line 1858, in _check_banner
    2016-04-06 10:24:01,155 3988 ERROR [paramiko.transport] raise SSHException('Error reading SSH protocol banner' + str(e))
    2016-04-06 10:24:01,155 3988 ERROR [paramiko.transport] SSHException: Error reading SSH protocol banner
    2016-04-06 10:24:01,155 3988 ERROR [paramiko.transport]

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/302641