file-logger: Prevent potential race when opening log files and change permission

file-logger: Prevent potential race when opening log files and change permission

This fixes a potential TOCTOU issue with opening log files.  The use of
`chown()` instead of `fchown()` could theoretically allow modifying the
ownership of an unintended file.

The log file now also is not world-readable anymore.

Also, the patch fixes the log groups for the two `(f)chown()` errors.

Fixes: d35d6691807d ("Make syslog and file loggers configurable at runtime")