Unify logger.conf and the fallback code

[bocekm]

• use logging.Formatter.converter = time.gmtime for both the file config and fallback config to have the same (UTC) time, in both cases
• unify log levels, using the fallback as the ones to use also in the conf file

[centos-ci]

Can one of the admins verify this patch?

[leapp-bot]

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[fernflower]

@oamg/developers Do we still want this? I'd rather close and reopen on demand.