docs: def capture_guest(userid):
      """Caputre a virtual machine image.
  
      Input parameters:
      :userid:   USERID of the guest, last 8 if length > 8
  
      Output parameters:
      :image_name:      Image name that captured
      """
      # check power state, if down, start it
      ret = sdk_client.send_request('guest_get_power_state', userid)
      power_status = ret['output']
      if power_status == 'off':
          sdk_client.send_request('guest_start', userid)
          # TODO: how much time?
          time.sleep(1)
  
      # do capture
      image_name = 'image_captured_%03d' % (time.time() % 1000)
      sdk_client.send_request('guest_capture', userid, image_name,
                              capture_type='rootonly', compress_level=6)
      return image_name