public static List<Path> getReferenceFilePaths(final FileSystem fs, final Path familyDir)
    throws IOException {
    return getFilePaths(fs, familyDir, new ReferenceFileFilter(fs));
  }
Given a particular region dir, return all the familydirs inside it
@param fs        A file system for the Path
@param regionDir Path to a specific region directory
@return List of paths to valid family directories in region dir.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/FSUtils.java