Use qWaitForWindowActive() where it is required.

Prepare a change in qtbase in which the implementation
of qWaitForWindowShown() will be changed to
qWaitForWindowExposed() instead of qWaitForWindowActive().
Try to stabilize further tests by introduing
wait functions instead of calls to qApp->processEvents().

Change-Id: I9825885430d78be1610a3fe20023fad24aaacba9
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>