Don't grab opts/pillar values when there is an explicit default file

Simple fix for bug #11133. If a defaults file is *explicitly* passed in at the same time that a mysql.user (etc) exists in opts/pillar, then the opts/pillar user will override the default file instead of the other way around. This change would fix this, but could in theory break things for older version. The ideal solution would be to actually parse the defaults file, but that seems way more error prone.