ipatests: fix expectations of `ipa trust-find` output for trust with root domain
    
    Test was expecting that when trust is established with forest root, than all
    three AD domains should be found when quering trust-find for that domain.
    Actually only root domain and its subdomain should be returned, without
    the tree domain.
    
    Related to https://pagure.io/freeipa/issue/7889
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>