Description

Cleanup a few basic things like:

• using shutil.rmtree() over rm -rf subprocess call
• clean up all the coverage data from the Makefile (make clean)
• Use the more readable text=True alias to subprocess calls (over universal_newlines=True) – it's available since Python 3.7
• Improve parameter passing to networkctl, accounting for network interfaces names that contain a leading -

Checklist

• Runs make check successfully.
• Retains 100% code coverage (make check-coverage).
• New/changed keys in YAML format are documented.
• (Optional) Adds example YAML for new feature.
• (Optional) Closes an open bug in Launchpad.