tests: Potential improvements to new CI setup #16664

Following #16582 and #16623, there are some potential improvements that could be made to the new CI setup:

• It'd be handy if the Docker containers were named. amd64_qt is more useful than peaceful_rubin once there are a bunch floating around. Done in #18081.
• Maybe we could stop (although not destroy) containers automatically after successful completion of the tests?
• The ci is generally assuming the the folder is a fresh git clone. If needed, that can be changed later on, but better not part of this pull.

When running locally any previous in-tree build artifacts are passed into the ci system. Instead of choking on them, the ci system should run make distclean if such artifacts exist.

suggested by @JeremyRubin in #17423 (comment)

Is this issue still relevant after what I understand to be a switch from Travis CI to Cirrus CI? I'm a first-time contributor and would like to work on this issue if it's still of use.