revert the visibility of interface AllocationFileLoaderService.Listener to public for outside usage

Hive/src/shims/scheduler/src/main/java/org/apache/hadoop/hive/schshim/FairSchedulerShim.java:[45,67] 
org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.AllocationFileLoaderService.Listener is not public in 
org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.AllocationFileLoaderService; cannot be accessed from outside package

allocsLoader.setReloadListener(new AllocationFileLoaderService.Listener() {
      @Override
      public void onReload(AllocationConfiguration allocs) {
        allocConf.set(allocs);
      }
    });