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>