idviews: Catch errors on unsuccessful AD object lookup when resolving object name to anchor
    
    When resolving non-existent objects, domain validator will raise ValidationError. We need
    to anticipate and properly handle this case.
    
    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>