void setReadyDelayed(long untilMs) {
            readyDelayedUntilMs = untilMs;
        }
This is a dumbed down version of {@link MetadataUpdater} which is used to facilitate
metadata tracking primarily in order to serve {@link KafkaClient#leastLoadedNode(long)}
and bookkeeping through {@link Metadata}. The extensibility allows AdminClient, which does
not rely on {@link Metadata} to do its own thing.
clients/src/test/java/org/apache/kafka/clients/MockClient.java