fix(updater): make clean-up job more robust / easier to debug

[joshtrichards]

• Resolves: n/a

Summary

On occasion there have been vague reports about the updater backup folder clean-up job (#9855) seemingly not, well, cleaning up. This adjusts the logging a bit and checks the return value of the deletions to give the admin (or us) a potentially better chance of figuring out what is going on.

TODO

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)