Remove context.Context from request.Request (#2726)

* Remove context.Context from request.Request

This removes the context from request.Request and makes all the changes
in the code to make it compile again. It's all mechanical. It did
unearth some weirdness in that the context was kept in handler structs
which may cause havoc with concurrently handling of requests.

Fixes #2721

Signed-off-by: Miek Gieben <miek@miek.nl>

* Make test compile

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/kubernetes/kubernetes_test.go

@@ -1,6 +1,7 @@
 package kubernetes
 
 import (
+	"context"
 	"testing"
 
 	"github.com/coredns/coredns/plugin"
@@ -281,7 +282,7 @@ func TestServices(t *testing.T) {
 			Req:  &dns.Msg{Question: []dns.Question{{Name: test.qname, Qtype: test.qtype}}},
 			Zone: "interwebs.test.", // must match from k.Zones[0]
 		}
-		svcs, e := k.Services(state, false, plugin.Options{})
+		svcs, e := k.Services(context.TODO(), state, false, plugin.Options{})
 		if e != nil {
 			t.Errorf("Test %d: got error '%v'", i, e)
 			continue