Support shutting down Samza job through coordinator stream

We have seen some use cases where people want to shutdown the Samza Job through another Samza Job. For example, after Samza job2 catches up Samza job1, job2 wants to shutdown job1. One of those cases was discussed here.

After SAMZA-448, we can easily meet this requirement – have the coordinator stream to accept a shutdown config/signal, and AM decides to shutdown all containers gracefully.