code: def remove_all_workers(self):
      for proc in self.worker_process:
          os.killpg(os.getpgid(proc.pid), signal.SIGTERM)
  
imports: import unittest
  from parl.utils import get_free_tcp_port
  from parl.utils import is_port_available
  from parl.utils import logger
  import multiprocessing
  from parl.remote.master import Master
  from parl.remote.worker import Worker
  from parl.remote.client import disconnect
  from parl.remote import remote_constants
  import time
  import os
  import signal
  import psutil
  import subprocess
label_desc: Use image node_id 7 for calling the XparlTestCase obj's underlying member method code with example usage: obj.remove_all_workers() without return types