Small improvements to the mirror tests
- Add a listing of Python dependencies needed for the tests
- Add a canonical way to environment variables for the tests
- Use logging to record tests progression
- Raise timeouts for replaying, shut down and storage access
- Use a dedicated network for Docker swarm
- Remove an unused Docker image from the generation process
- Add troubleshooting tips to the test documentation
Migrated from D8556 (view on Phabricator)