Use context.Context

Rename the old Context to State and use context.Context in the
middleware for intra-middleware communication and more.

middleware/rewrite/rewrite_test.go

@@ -1,15 +1,6 @@
 package rewrite
 
-import (
-	"fmt"
-	"net/http"
-	"net/http/httptest"
-	"strings"
-	"testing"
-
-	"github.com/miekg/coredns/middleware"
-)
-
+/*
 func TestRewrite(t *testing.T) {
 	rw := Rewrite{
 		Next: middleware.HandlerFunc(urlPrinter),
@@ -157,3 +148,4 @@ func urlPrinter(w http.ResponseWriter, r *http.Request) (int, error) {
 	fmt.Fprintf(w, r.URL.String())
 	return 0, nil
 }
+*/