create dbvis_add_db_admin.rb

Dbvisulaizer offers a command line functionality to execute SQL pre-configured databases (With GUI).
The remote database can be accessed from the command line without the need to authenticate.
The module abuses this functionality to create an administrator in the database if DB user rights allow it.
You should be able to use ```cmd_exec``` instead of using execute() and read(). The return value of ```cmd_exec``` is the command output, so you can just regex that instead.