docs: public static void checkRequired(OptionSet options, List<String> opts)
              throws VoldemortException {
          List<String> optCopy = Lists.newArrayList();
          for(String opt: opts) {
              if(options.has(opt)) {
                  optCopy.add(opt);
              }
          }
          if(optCopy.size() < 1) {
              System.err.println("Please specify one of the following options:");
              for(String opt: opts) {
                  System.err.println("--" + opt);
              }
              Utils.croak("Missing required option.");
          }
          if(optCopy.size() > 1) {
              System.err.println("Conflicting options:");
              for(String opt: optCopy) {
                  System.err.println("--" + opt);
              }
              Utils.croak("Conflicting options detected.");
          }
      }