void processPid() {
    String pidFile = System.getProperty(IoTDBConstant.IOTDB_PIDFILE);
    if (pidFile != null) {
      new File(pidFile).deleteOnExit();
    }
  }
Register services and set up DataNode.

@throws StartupException if start up failed.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/service/DataNode.java