Update Qt Installer-Framework related build scripts

- Support Qt5 based builds (default behavior)
- Support Qt4 based builds
- Cleanup & refactor

Task-Id: QTBUG-41816
Change-Id: I656cd6f1ebbf1fa5f3e10810a262ed3f0f1f89bc
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>