Apache Kafka module has awkward default configuration for brokerId

[copumpkin]

The default configuration makes brokerId default to 0, which means you can only run one node with the default and then it'll complain that the broker with that ID is already registered. -1 seems like a better default, since that tells Kafka to pick a broker ID automatically.

cc @ragnard @shlevy

[shlevy]

👍