code: Map<String, List<String>> getBlackListedTrackers() {
  
      Map<String, List<String>> blackListedTrackers
          = new HashMap<String, List<String>>();
  
      for (Map.Entry<String,List<String>> e : trackerToFailuresMap.entrySet()) {
         if (e.getValue().size() >= maxTaskFailuresPerTracker) {
           blackListedTrackers.put(e.getKey(), e.getValue());
         }
      }
      return blackListedTrackers;
    }
docs: Get the black listed trackers for the job and corresponding errors.
  
  @return Map of blacklisted tracker names and the errors for each tracker
  that triggered blacklisting