In the new version of PyYAML the API changed to be more explicit. Now
the default value for the Loader is None, see:
https://github.com/yaml/pyyaml/blob/5.1/lib3/yaml/__init__.py#L103
The load is unsafe. It's better to use safe_load function.
Change-Id: Ia1cd16f2ff970ca220a266c99b6554dd4254ebd9