Add a get_all_list_data utility function that uses a get_next generator ...

...function to retrieve all json data for methods that return a list and support pagination.  Include tests and function doc.
Can json_data be an empty list (if so, the 'if json_data' will evaluate to false). 

I also seem to remember that the Python book had an 'or' notation for this kind of pattern. I may have the details wrong, but could you do 'return_value = json_data or mock.Default'? It's not really a big deal either way.