config: provide defaults for `xmlrpc_uri`, `ldap_uri` and `basedn`
Derive the default value of `xmlrpc_uri` and `ldap_uri` from `server`.
Derive the default value of `basedn` from `domain`.
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>