Check for the clipboard manager when looping due to app quiting

Check for the clipboard manager when looping due to app quiting

One can be extremely unlucky and on session logout get this:
 * All apps are going down
 * A Qt app checks if the clipboard manager is there to yield its clipboard contents
   * The clipboard manager is still there
 * Then just after that check, the clipboard manager finishes because of the session end
 * This means the Qt app will loop for 5 seconds trying to yield its clipboard contents
   to a clipboard manager that is not there anymore

Change-Id: Ia89670d4deb72f12e660a0d7aa5b2d212955d6fe
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>