idviews: Update the referential plugin config to watch for ipaAssignedIDView
    
    We need the referential plugin config to watch for changes in the ID view
    objects, since hosts refer to them in ipaAssignedIDView attribute.
    
    Part of: https://fedorahosted.org/freeipa/ticket/3979
    
    Reviewed-By: Petr Viktorin <pviktori@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>