Kafka Connect fails to create connector if single-broker Kafka cluster is configured for offsets.topic.replication.factor=3

If I mis-configure my single Kafka broker with `offsets.topic.replication.factor=3` (the default), Kafka Connect will start up absolutely fine (Kafka Connect started in the log file, `/connectors` endpoint returns HTTP 200). But if I try to create a connector, it (eventually) returns

{"error_code":500,"message":"Request timed out"}

There's no error in the Kafka Connect worker log at INFO level. More details: https://rmoff.net/2019/11/29/kafka-connect-request-timed-out/

This could be improved. Either at startup ensure that the Kafka consumer offsets topic is available and not startup if it's not, or at least log why the connector failed to be created.