This patch fixes a tight broker to controller reconnection loop that may happen during shutdown.

1. Node 1 and 2 (brokers) request controlled shutdown
2. Controller grants the shutdown
3. Controller itself shuts down (RaftManager shutdown)
4. Node 1 and 2 continue trying to heartbeat to the now-dead controller
5. They get stuck in this reconnection loop because the NodeToControllerRequestThread is still running and hasn't been shut down properly

The reconnection loop goes on for exactly 5 minutes, which is the shutdown timeout hard coded in KafkaBroker trait.

This is what I have from another test logs for one of the brokers:

    SIGTERM received: 14:39:46,282
    Actual shutdown completed: 14:44:46,385
    Time elapsed: 5 minutes and 0.103 seconds (approximately 5 minutes)

I acknowledge that this is unlikely to happen with brokers running on different machine, but not so unlikely when running tests locally on a single physical machine.

Signed-off-by: Federico Valeri <[email protected]>