@Override
  public void stop(final String why) {
    if (refreshChore != null) {
      LOG.debug("Stopping QuotaRefresherChore chore.");
      refreshChore.shutdown(true);
    }
    stopped = true;
  }
Cache that keeps track of the quota settings for the users and tables that are interacting with
it. To avoid blocking the operations if the requested quota is not in cache an "empty quota" will
be returned and the request to fetch the quota information will be enqueued for the next refresh.
TODO: At the moment the Cache has a Chore that will be triggered every 5min or on cache-miss
events. Later the Quotas will be pushed using the notification system.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/QuotaCache.java