code: public static String constructHadoopTags(Props props, String[] keys) {
      String[] keysAndValues = new String[keys.length];
      for (int i = 0; i < keys.length; i++) {
        if (props.containsKey(keys[i])) {
          keysAndValues[i] = keys[i] + ":" + props.get(keys[i]);
        }
      }
      Joiner joiner = Joiner.on(',').skipNulls();
      return joiner.join(keysAndValues);
    }
docs: Construct a CSV of tags for the Hadoop application.
  
  @param props job properties
  @param keys list of keys to construct tags from.
  @return a CSV of tags