updater: Adding --fix-broken stages

The updater will now try to fix broken packages before and after
dist-upgrade. This can help in some cases when there's something
hanging not configured or just part-installed.

Fixes https://github.com/KanoComputing/peldins/issues/721
Merge pull request #7 from KanoComputing/peldins-issue-721

updater: Adding --fix-broken stages