func newImageSource(tmpDir string, ref ostreeReference) (types.ImageSource, error) {
	return &ostreeImageSource{ref: ref, tmpDir: tmpDir, compressed: nil}, nil
}
func newImageSource(tmpDir string, ref ostreeReference) (types.ImageSource, error) {
	return &ostreeImageSource{ref: ref, tmpDir: tmpDir, compressed: nil}, nil
}
// newImageSource returns an ImageSource for reading from an existing directory.