separate database from database users
There needs to be a separate management system for mysql users, this way you could create read only databases and the like.
Id suggest leaving the add database form as it is, but allow the user to leave the database user empty, this would not create a new user.
Then have a separate list database users/edit database users page. Furthermore, allow a drill down approach when editing databases (new tab in edit database that has users for this database - similar to how DNS is navigated)
I'll pick this up and patch it in if no-one else covers it.