public int getCacheStats() {
    return cacheMisses.get();
  }
Fetches the ClusterId from FS if it is not cached locally. Atomically updates the cached copy
and is thread-safe. Optimized to do a single fetch when there are multiple threads are trying
get from a clean cache.
@return ClusterId by reading from FileSystem or null in any error case or cluster ID does not
        exist on the file system or if the server initiated a tear down.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/CachedClusterId.java