poseidon frequently sends to wrong broker

I added some debug logging to this fork https://github.com/sclasen/poseidon  which also contains some logic to actually read the ProduceResponse to determine if it was successful.  Sending to a topic with 32 partitions and replication factor 3. 

```
poseidon logs
KAFKADEBUG LEADER FOR 23 is 3867 
KAFKADEBUG api.3865.1 sending messages for broker 3867
KAFKADEBUG PRODUCE CORRELATION 1 from CLIENT api.3865.1 TO <ip:port of 3867>
```

```
kafka logs
Produce request with correlation id 1 from client api.3865.1 
on partition [<topic>,23] failed 
due to Leader not local for partition [<topic>,23] on broker 3867 (kafka.server.KafkaApis)
```

So poseidon is somehow getting confused about the leading broker.