fix window activation in tst_qmdiArea::subWindowActivated2

fix window activation in tst_qmdiArea::subWindowActivated2

QApplication::setActiveWindow doesn't activate the native window but
marks the widget as active inside Qt.
We need to use QWidget::activateWindow instead. See docs.

Also moved the activation call further down because on Windows a
minimized window cannot be activated using the activation-by-focus
fake we're currently using.

Change-Id: I752f6ada1f463931fa9cfb3c35f42dbec0207bfa
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>