server install: fix KDC PKINIT configuration
Set `pkinit_pool` in `kdc.conf` to a CA certificate bundle of all CAs known
to IPA.
Make sure `cacert.pem` is exported in all installation code paths.
Use the KDC certificate itself as a PKINIT anchor in `login_password`.
https://pagure.io/freeipa/issue/6831
Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>