Enhance the collect_primary_datasets() method to allow assignment of the defined output parameter for 3rd-party tools that manage tool outputs internally.
Make dynamic discovery of output datasets deterministic.

Should aid in testing and ... lets say ... reproducibility because that is popular in these parts.
Implement tool test demonstrating pull request 569.

The new assign_primary_output attribute on discover_datasets tag.
Merge pull request 569 with test implemented to demonstrate.