docs: def is_instance_running(self, instance_id):
          """Checks if the instance is up and running.
  
          :param str instance_id: instance identifier
  
          :return: bool - True if running, False otherwise
          """
          self._restore_from_storage(instance_id)
          if self._start_failed:
              raise Exception('is_instance_running for node %s: failing due to'
                              ' previous errors.' % instance_id)
          try:
              v_m = self._qualified_name_to_vm(instance_id)
              if not v_m:
                  raise Exception("Can't find instance_id %s" % instance_id)
          except Exception:
              log.error(traceback.format_exc())
              raise
          return v_m._power_state == 'Started'