@Override
        public void modifyConfigs(Seq<Properties> props) {
            super.modifyConfigs(props);
            for (int i = 0; i < props.length(); i++) {
                props.apply(i).putAll(clusterConfig.perServerOverrideProperties().getOrDefault(i, Collections.emptyMap()));
            }
        }
Restart brokers with given cluster config.

@param clusterConfig clusterConfig is optional. If left Optional.empty(), brokers will restart without
                     reconfiguring configurations. Otherwise, the restart will reconfigure configurations
                     according to the provided cluster config.
core/src/test/java/kafka/test/junit/ZkClusterInvocationContext.java