@Override
  public String toString() {
    return String.format("%s:%s", systemName, clientId);
  }
Compare two String offsets.
Note. There is a method in KafkaSystemAdmin that does that, but that would require instantiation of systemadmin for each consumer.
@return see {@link Long#compareTo(Long)}
samza-kafka/src/main/java/org/apache/samza/system/kafka/KafkaSystemConsumer.java