Improve guest log collection

[happz]

• Setup/teardown methods - virtual has them, artemis needs them, make it official.
• Many warnings turned exceptions, too many issues went silently. This was expected, we now have support for logs in 3 plugins, we can identify where we want to stop and what we are willing to tolerate.
• Storing logs simplified - no dir/file duality, always given a file path.
• artemis needs to trigger collection, therefore it adds setup() implementation.
• Nicer logging, include log name in exceptions.
• Log name vs log filename, two different things.
• Some extra documentation, including a life cycle draft.

Pull Request Checklist

• [ ] implement the feature
• [ ] write the documentation
• [ ] extend the test coverage
• [ ] update the specification
• [ ] adjust plugin docstring
• [ ] modify the json schema
• [ ] mention the version
• [ ] include a release note