Factor out clicking of update and akonadi notifications in KDE
    
    There are three places where we basically want to click away
    pop-up update notifications and the buggy akonadi_migration_agent
    notification if it's there, in KDE tests. Let's share this code
    between them, and also let's record soft failures for the buggy
    cases in the desktop_notifications test.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>