fix(Logger): Warn on invalid loglevel configuration option

[susnux]

Summary

When the configuration is not a valid integer do not silently fallback to warn, instead try to cast it (might be more what the admin wanted to configure, e.g. allows '0' when 0 was meant).
And if the value is invalid do handle it not silently but at least put a warning in the log (even we do not have access to the logger we can put it in the error log.

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)

[skjnldsv]

Thank you for the additional fix :)