private String roles(int node) {
            if (nodes.isCombined(node)) {
                return "broker,controller";
            }
            if (nodes.controllerNodes().containsKey(node)) {
                return "controller";
            }
            return "broker";
        }
This class manages a future which is completed with the proper value for
controller.quorum.voters once the randomly assigned ports for all the controllers are
known.
core/src/test/java/kafka/testkit/KafkaClusterTestKit.java