with_dict_lists iterator to loop over lists nested in lists of dictionaries

This improves the ability to work on EC2 related tasks, where you may have run an EC2 task that creates many items with another list of items.

Documentation explaining what happens has been added to the relevant wiki page https://github.com/randomvariable/ansible/blob/with_dict_lists/docsite/rst/playbooks_loops.rst#iterating-over-a-nested-list-as-the-output-of-register .

A better plugin name is welcome.