(PUP-3462) Hiera scope: add the key 'calling_class_path' 

calling_class_path is calling_class with :: replaced by a /

This enables to have the class hiera yaml files in directories and enables to have class based hiera data on windows which does not allow ":" in path names.
prefer `||` over `or` - yes, I realize the code had `or` in it before.