QtIFW

Fix issue with accessing install target directory.

In case we run as installer, do not look into the installation
target directory to read the package XML file. This needs only
be done to get installed packages, read the application name
and version to compare updates and online components against.

Change-Id: Ie5b82854e41dc2f11ae5668c5839351c2fc52e04
Reviewed-by: Jarek Kobus <jaroslaw.kobus@theqtcompany.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@theqtcompany.com>