public static byte[] tail(final byte[] a, final int length) {
    if (a.length < length) {
      return null;
    }
    byte[] result = new byte[length];
    System.arraycopy(a, a.length - length, result, 0, length);
    return result;
  }
Make a new byte array from a subset of bytes at the tail of another.
@param a      array
@param length amount of bytes to snarf
@return Last <code>length</code> bytes from <code>a</code>
hbase-common/src/main/java/org/apache/hadoop/hbase/util/Bytes.java