Updates logrotate.conf for Debian

/var/log group in Ubuntu is syslog. This formula breaks
Ubuntu logrotate.

logrotate/files/Debian/logrotate.conf

 # rotate log files weekly
 weekly
 
+{% if grains['os'] == "Ubuntu" %}
+# use the syslog group by default, since this is the owning group
+# of /var/log/syslog.
+su root syslog
+{% endif %}
+
 # keep 4 weeks worth of backlogs
 rotate 4