[1458] unify a message ID and its brief description (on 'refused' vs 'denied')

adopted denied as it was used in BIND 9's log message.

src/lib/python/isc/ddns/libddns_messages.mes

@@ -50,7 +50,7 @@ configuration of those clients to suppress the requests.  As specified
 in Section 3.1 of RFC2136, the receiving server will return a response
 with an RCODE of NOTAUTH.
 
-% LIBDDNS_UPDATE_REFUSED update client %1 for zone %2 denied
+% LIBDDNS_UPDATE_DENIED update client %1 for zone %2 denied
 Informational message.  An update request was denied because it was
 rejected by the zone's update ACL.  When this library is used by
 b10-ddns, the server will respond to the request with an RCODE of

src/lib/python/isc/ddns/session.py

@@ -186,7 +186,7 @@ class UpdateSession:
         action = acl.execute(isc.acl.dns.RequestContext(
                 (self.__client_addr[0], self.__client_addr[1]), self.__tsig))
         if action == REJECT:
-            logger.info(LIBDDNS_UPDATE_REFUSED,
+            logger.info(LIBDDNS_UPDATE_DENIED,
                         ClientFormatter(self.__client_addr, self.__tsig),
                         ZoneFormatter(zname, zclass))
             raise UpdateError('rejected', zname, zclass, Rcode.REFUSED(), True)