Always set ca_host when installing replica
    
    ipa-replica-install only set ca_host in its temporary
    /etc/ipa/default.conf, when it wasn't installing a replica with CA. As a
    consequence, the replica installer was picking a random CA server from
    LDAP.
    
    Always set the replication peer as ca_host. This will ensure that the
    installer uses the same replication peer for CA. In case the replication
    peer is not a CA master, the installer will automatically pick another
    host later.
    
    See: https://pagure.io/freeipa/issue/7566
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>