poll() timeout not enforced when connecting to 0.10.0 broker

In 0.10.1, heartbeat thread and new poll timeout max.poll.interval.ms got introduced via KIP-62. In 0.10.2, we added client-broker backward compatibility.

Now, if a 0.10.2 client connects to a 0.10.0 broker, the broker only understand the heartbeat timeout but not the poll timeout, while the client is still using the heartbeat background threat. Thus, the new client config max.poll.interval.ms is ignored.

In the worst case, the polling threat might die while the heartbeat thread is still up. Thus, the broker would not timeout the client and no rebalance would be triggered while at the same time the client is effectively dead not making any progress in its assigned partitions.