Runs the playbook and returns True if it completes successfully on 
  a single host.

def RunPlaybookOnHost(playbook_path, host, private_key, extra_vars=None):
  """ 
  Runs the playbook and returns True if it completes successfully on 
  a single host.
  """
  return RunPlaybookOnHosts(playbook_path, [host], private_key, extra_vars)