The consensus on my last question is that it wasn't an issue - ports will be bound before being used.  So nothing has been changed in this respect.

This ticket is now ready for first review.  As parallelising all the tests will change a large number of files, I'd prefer to get a review done of the framework changes and the few tests that have already been converted before proceeding with the rest of the changes.

I suggest that the review first start with bin/tests/system/README.  This has been more or less completely rewritten, and should provide context for the review of the remaining files.