docs: public static void main(String... args) throws Exception {
          if (args.length != 1) {
              throw new Exception("pass one parameter, $JENKINS_HOME");
          }
          File root = new File(args[0]);
          File jobs = new File(root, "jobs");
          if (!jobs.isDirectory()) {
              throw new FileNotFoundException("no such $JENKINS_HOME " + root);
          }
          new RunIdMigrator().unmigrateJobsDir(jobs);
      }