Fix default qt version used for IFW

Latest ifw requires 4.8.1 or newer. Actually we've been explicitly
using the 4.8.4 package anyway for the official installers ...

Task-number: QTIFW-314
Change-Id: Icf58d99a085c4a13cf9853c9cb342496a9ed59f2
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
Reviewed-by: Andreas Holzammer <andreas.holzammer@kdab.com>