code: public static void checkRequired(OptionSet options, String opt1, String opt2)
              throws VoldemortException {
          List<String> opts = Lists.newArrayList();
          opts.add(opt1);
          opts.add(opt2);
          checkRequired(options, opts);
      }
docs: Checks if there's exactly one option that exists among all possible opts.
  
  @param options OptionSet to checked
  @param opt1 Possible required option to check
  @param opt2 Possible required option to check
  @throws VoldemortException