Matches logrotate user to ownership of /var/log

Ownership of /var/log is root:syslog so the logrotate job needs to run as this user otherwise the service fails to start with the following error:-

error: skipping "/var/log/mysql.log" because parent directory has insecure permissions (It's world writable or writable by group which is not "root") Set "su" directive in config file to tell logrotate which user/group should be used for rotation.

notifempty will also help prevent otheer errors as by default Ubuntu doesn't use /var/log/mysql.log.