fix for NXDOMAIN becomes NOERROR

Copy the actual rcode from the response into our answer (it always set
NOERROR, so this should also work for other rcodes)

src/bin/resolver/resolver.cc

@@ -260,6 +260,7 @@ public:
                 Message incoming(Message::PARSE);
                 InputBuffer ibuf(buffer->getData(), buffer->getLength());
                 incoming.fromWire(ibuf);
+                message->setRcode(incoming.getRcode());
                 for_each(incoming.beginSection(Message::SECTION_ANSWER),
                          incoming.endSection(Message::SECTION_ANSWER),
                          SectionInserter(message, Message::SECTION_ANSWER));