public String zKConnectString() {
        return "127.0.0.1:" + zookeeper.port();
    }
The ZooKeeper connection string aka `zookeeper.connect` in `hostnameOrIp:port` format.
Example: `127.0.0.1:2181`.
<p>
You can use this to e.g. tell Kafka brokers how to connect to this instance.
streams/src/test/java/org/apache/kafka/streams/integration/utils/EmbeddedKafkaCluster.java