String getBarrierStatePath(String version) {
      return getBarrierPath(version) + BARRIER_STATE;
    }
Listener for changes to the Barrier state. It is subscribed by all participants of the barrier, including the
participant that creates the barrier.
Barrier state values are either DONE or TIMED_OUT. It only registers to receive on valid state change notification.
Once a valid state change notification is received, it will un-subscribe from further notifications.
samza-core/src/main/java/org/apache/samza/zk/ZkBarrierForVersionUpgrade.java