So, to make local containers play nice with testing:
build and release plugins should perform the move-to-old step themselves, rather than being handled by cleanup like it is right now.
This plugin will be split into plushu-deploy-app-local and plushu-local-app-container. The latter will take all the start-local-app implementation stuff, while the former will handle the abstract handle-deployment-by-starting-the-new-release-locally logic.
plushu-deploy-app-local can be swapped out for a plugin that implements CI-esque tests, and will fail the build and roll back if the built image does not pass the tests.
What hook should this have for tests?