message: fix python2 compatibility
  String literal interpolation is not supported by Python < 3.6
diff: @@ -90,7 +90,7 @@ def find_all(path, serial_number,
  fp.seek(0)
  json_data = json.load(fp)
  except:
  - logger.debug(f"Failed load JSON cache file {cache_path}")
  + logger.debug("Failed load JSON cache file {}".format(cache_path))
  # Fallback to loading JSON from device
  if json_data is None:
  @@ -108,11 +108,11 @@ def find_all(path, serial_number,
  # Save JSON to cache
  if not cache_path is None:
  - logger.debug(f"Creating new JSON cache file {cache_path}")
  + logger.debug("Creating new JSON cache file {}".format(cache_path))
  os.makedirs(cache_dir, exist_ok=True)
  with open(cache_path, 'w+') as json_cache:
  json_cache.write(json_string)
  - logger.debug(f"Saved JSON to cache file {cache_path}")
  + logger.debug("Saved JSON to cache file {}".format(cache_path))
  channel._interface_definition_crc = json_crc16
  