Minor improvements on the demo

[emmanuelbernard]

It would be nice to have a script or some instructions to clean the relevant resources in /tmp and deploy between runs. (Moved to #3)

Also when I stop the grid while still watching a topic, I receive a lot of stacktraces in a loop

$ bin/grid watch entity-batches
[2015-01-28 15:38:55,778] WARN Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect (org.apache.zookeeper.ClientCnxn)
java.net.ConnectException: Connection refused
        at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
        at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:712)
        at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1146)
[2015-01-28 15:38:56,669] WARN Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect (org.apache.zookeeper.ClientCnxn)
java.net.ConnectException: Connection refused
        at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
        at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:712)
        at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1146)
[2015-01-28 15:38:56,782] WARN Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect (org.apache.zookeeper.ClientCnxn)
java.net.ConnectException: Connection refused
        at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
        at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:712)
        at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1146)

[rhauch]

Yes, you will get these exceptions until Kafka comes back up. There's really no way to tell the difference between Kafka going down permanently or temporarily, and consumers (inducing the watch command) will in a normal environment just continue watching until it comes back up.

BTW, the watch command is just running one of Kafka's utilities. Granted, the error output could be made a bit more friendly; that's something that could be done in the future with a custom utility.