@Override
        public Option<Properties> serverSaslProperties() {
            if (clusterConfig.saslServerProperties().isEmpty()) {
                return Option.empty();
            } else {
                Properties props = new Properties();
                props.putAll(clusterConfig.saslServerProperties());
                return Option.apply(props);
            }
        }
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