Extract the VQA V2 feature data set to directory unless it's there.

def _get_vqa_v2_image_feature_dataset(
    directory, feature_url, feature_filename="mscoco_feat.tar.gz"):
  """Extract the VQA V2 feature data set to directory unless it's there."""
  feature_file = generator_utils.maybe_download_from_drive(
      directory, feature_filename, feature_url)
  with tarfile.open(feature_file, "r:gz") as feature_tar:
    feature_tar.extractall(directory)