Stabilize tst_QShortcut

show() on a window is asynchronous.  Wait for it to complete before
continuing with the test.

Note the test already contained code for this, but it was inside of
a Q_WS_X11 block, making it dead code in Qt 5.

Change-Id: I06f892eea86278c56b1773a7e968bbe065f86260
Reviewed-by: Kalle Lehtonen <kalle.ju.lehtonen@nokia.com>

tests/auto/gui/kernel/qshortcut/tst_qshortcut.cpp

@@ -221,9 +221,7 @@ void tst_QShortcut::initTestCase()
     mainW->setFixedSize( 100, 100 );
     mainW->setCentralWidget( edit );
     mainW->show();
-#ifdef Q_WS_X11
-    qt_x11_wait_for_window_manager(mainW);
-#endif
+    QTest::qWaitForWindowShown(mainW);
     mainW->activateWindow();
     QTest::qWait(100);
     connect( mainW->statusBar(), SIGNAL(messageChanged(const QString&)),