docs: def exec_prog(args):
      """Run a subprocess, check for .OK and raise error if does not exist.
  
      args:  list of arguments, for value is the command to execute.
      """
  
      program_name = args[0]
      logging.info(" ".join(args))
      output = subprocess.check_output(args, stderr=subprocess.STDOUT)
      if not os.access(program_name+".OK", os.F_OK):
          logging.error("No {}.OK file?".format(program_name))
          raise subprocess.CalledProcessError(-1, ' '.join(args), output)
      os.unlink(program_name+".OK")
      if os.access(program_name+".FAILED", os.F_OK):
          os.unlink(program_name+".FAILED")
      return output