replica install: set the same master as preferred source for domain and CA
    
    During ipa-replica-install, the installer creates a ReplicaConfig
    object that contains a config.ca_host_name attribute, built from
    api.env.ca_host.
    This attribute is used as preferred source when asking the DNS for a CA
    master from which to initialize the CA instance
    (see commit 8decef33 for master selection and preferred host).
    
    In most of the cases, /etc/ipa/default.conf does not contain any
    definition for ca_host. In this case, api.env.ca_host is set to
    the local hostname.
    As a consequence, replica install is trying to use the local host
    as preferred source (which does not have any CA yet), and the method
    to find the CA source randomly picks the CA in the DNS.
    
    With the fix, the master picked for domain replication is also used as
    preferred source for CA/KRA.
    
    Fixes: https://pagure.io/freeipa/issue/7744
    Reviewed-By: Christian Heimes <cheimes@redhat.com>