new data query associations need to prompt for variable vals

[ehall]

When the user associates a data query to a device, Cacti immediately runs the query so as to build the indexed array.

If/when support for script data variables is added, Cacti will need to obtain those variables before the script is initially executed.

This behavior should reflect the behavior we see now whenever a new indexed entry is graphed (a dialog prompts for variables first), except that it should also prompt whenever a new data query is added if that query has variables defined.