mw/federation: add federation back as separate mw for k8s (#929)

* mw/federaration

This PR add the federation back as a middleware to keep it more
contained from the main kubernetes code.

It also makes parseRequest less import and pushes this functionlity down
in the k.Entries. This minimizes (or tries to) the importance for the
qtype in the query. In the end the qtype checking should only happen
in ServeDNS - but for k8s this might proof difficult.

Numerous other cleanup in code and kubernetes tests.

* up test coverage

middleware/federation/nonwriter.go

@@ -0,0 +1,22 @@
+package federation
+
+import (
+	"github.com/miekg/dns"
+)
+
+// NonWriter is a type of ResponseWriter that captures the message, but never writes to the client.
+type NonWriter struct {
+	dns.ResponseWriter
+	Msg *dns.Msg
+}
+
+// NewNonWriter makes and returns a new NonWriter.
+func NewNonWriter(w dns.ResponseWriter) *NonWriter { return &NonWriter{ResponseWriter: w} }
+
+// WriteMsg records the message, but doesn't write it itself.
+func (r *NonWriter) WriteMsg(res *dns.Msg) error {
+	r.Msg = res
+	return nil
+}
+
+func (r *NonWriter) Write(buf []byte) (int, error) { return len(buf), nil }