code: def terminate(self, nodes=None):
          
          if not self.is_connected():
              return None
  
          nodes = nodes or self.nodes
          failed_kill = []
  
          result = self.gce.ex_destroy_multiple_nodes(nodes, poll_interval=1, ignore_errors=False)
  
          # Verify whether all instances have been terminated.
          for i, success in enumerate(result):
              if success:
                  logging.info('Successfully destroyed: %s', nodes[i].name)
              else:
                  logging.error('Failed to destroy: %s', nodes[i].name)
                  failed_kill.append(nodes[i])
  
          return failed_kill
docs: Destroy one or many nodes.
  
          :param   nodes: Nodes to be destroyed.
          :type    nodes: ``list``
  
          :return: List of nodes which failed to terminate.
          :rtype:  ``list``