certs: do not implicitly create DS pin.txt
    
    Do not implicitly create DS pin.txt in `CertDB.init_from_pkcs12()`, create
    it explicitly in `DSInstance.__enable_ssl()`.
    
    This stops the file from being created in /etc/httpd/alias during classic
    replica install.
    
    https://pagure.io/freeipa/issue/4639
    
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>