(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.
I'm thinking more like 
`[CALLING_CLASS, CALLING_CLASS_PATH, CALLING_MODULE].include? key`