ovirt: Don't try to use [ovirt] if jsessionid is not set
    
    If jsessionid is not set in the .vv file and we try to use anyway the
    REST API, an authentication dialog will be shown by remote-viewer, which
    is very unwelcome. If we don't have a jsessionid set, we know we won't
    be able to silently login to the REST API, so don't try to set a foreign
    menu when it's not set.