code: private String getSparkLibDir(final String sparkHome) {
      // sparkHome should have already been checked when this method is invoked
      final File homeDir = new File(sparkHome);
      File libDir = new File(homeDir, "lib");
      if (libDir.exists()) {
        return libDir.getAbsolutePath();
      } else {
        libDir = new File(homeDir, "jars");
        if (libDir.exists()) {
          return libDir.getAbsolutePath();
        } else {
          throw new RuntimeException("SPARK lib dir does not exist.");
        }
      }
    }
docs: Given the dir path of Spark Home, return the dir path of Spark lib.
  It is either sparkHome/lib or sparkHome/jars based on the version of
  Spark chosen by user.
  
  @param sparkHome dir path of Spark Home
  @return dir path of Spark lib