Checks if the instance is up and running.

        :param str instance_id: instance identifier

        :return: bool - True if running, False otherwise

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'