cert-request: generalise _san_dnsname_ips for arbitrary cname depth
Generalise _san_dnsname_ips to allow arbitrary cname depths. This
also clarifies the code and avoids boolean blindness. Update the
call site to maintain the existing behvaiour (one cname allowed).
Part of: https://pagure.io/freeipa/issue/7451
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>