mw/kubernetes: add reverse_test.go (#922)

This PR adds a reverse tests that copies some of it from the main
integration test. This aids in local testing because you don't need
a full k8s setup running.

It does the most minimal testing, a successful return and a nodata
response that includes the SOA for in-addr.arpa.

middleware/kubernetes/handler.go

@@ -21,8 +21,7 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 	m := new(dns.Msg)
 	m.SetReply(r)
 	m.Authoritative, m.RecursionAvailable, m.Compress = true, true, true
-	// Check that query matches one of the zones served by this middleware,
-	// otherwise delegate to the next in the pipeline.
+
 	zone := middleware.Zones(k.Zones).Matches(state.Name())
 	if zone == "" {
 		if k.Fallthrough {