[fuel-devops] revert-resume action of dos.py throws exception when tries to reach admin node

When fuel-devops tries revert and resume a environment without the admin node, execution finished by exception

Expected result:

Do nothing if environment doesn't have the admin node.

Actual result:

$ dos.py revert-resume fuel-ccp k8s_deployed
2016-08-02 15:35:58 - INFO - libvirt_driver.py:1463 -- Revert node-1 (paused) to internal snapshot k8s_deployed
2016-08-02 15:36:07 - INFO - libvirt_driver.py:1463 -- Revert node-2 (paused) to internal snapshot k8s_deployed
2016-08-02 15:36:16 - INFO - libvirt_driver.py:1463 -- Revert node-3 (paused) to internal snapshot k8s_deployed
2016-08-02 15:36:23 - INFO - libvirt_driver.py:1463 -- Revert node-4 (paused) to internal snapshot k8s_deployed
2016-08-02 15:36:31 - INFO - libvirt_driver.py:1463 -- Revert node-5 (paused) to internal snapshot k8s_deployed
Time synchronization is starting
Traceback (most recent call last):
  File "/home/dtyzhnenko/devops-venv/bin/dos.py", line 6, in <module>
    exec(compile(open(__file__).read(), __file__, 'exec'))
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/bin/dos.py", line 22, in <module>
    main()
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/shell.py", line 630, in main
    Shell(args).execute()
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/shell.py", line 55, in execute
    self.commands.get(self.params.command)(self)
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/shell.py", line 179, in do_revert_resume
    self.do_timesync()
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/shell.py", line 164, in do_timesync
    cur_time = sync_time(self.env, nodes, skip_sync=True)
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/helpers/retry.py", line 56, in wrapper
    return func(*args, **kwargs)
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/helpers/ntp.py", line 37, in sync_time
    with GroupNtpSync(env, node_names) as g_ntp:
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/helpers/ntp.py", line 294, in __init__
    remote = get_node_remote(env, node_name)
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/helpers/helpers.py", line 204, in get_node_remote
    name=node_name).interfaces[0].mac_address)
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/helpers/helpers.py", line 235, in get_slave_ip
    admin_ip = get_admin_ip(env)
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/helpers/helpers.py", line 216, in get_admin_ip
    return env.get_node(name='admin').get_ip_address_by_network_name('admin')
  File "/home/dtyzhnenko/workspace/fuel/fuel-devops/devops/models/environment.py", line 519, in get_node
    raise DevopsObjNotFound(Node, *args, **kwargs)
devops.error.DevopsObjNotFound: devops.models.node.Node(name='admin') does not exist in database.