DNSSEC: schema
    
    Tickets:
    https://fedorahosted.org/freeipa/ticket/3801
    https://fedorahosted.org/freeipa/ticket/4417
    
    Design:
    https://fedorahosted.org/bind-dyndb-ldap/wiki/BIND9/Design/DNSSEC
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: David Kupka <dkupka@redhat.com>