Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/dnstap/msg/msg_test.go

@@ -0,0 +1,42 @@
+package msg
+
+import (
+	"net"
+	"reflect"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/request"
+
+	tap "github.com/dnstap/golang-dnstap"
+	"github.com/miekg/dns"
+)
+
+func testRequest(t *testing.T, expected Data, r request.Request) {
+	d := Data{}
+	if err := d.RemoteAddr(r.W.RemoteAddr()); err != nil {
+		t.Fail()
+		return
+	}
+	if d.SocketProto != expected.SocketProto ||
+		d.SocketFam != expected.SocketFam ||
+		!reflect.DeepEqual(d.Address, expected.Address) ||
+		d.Port != expected.Port {
+		t.Fatalf("expected: %v, have: %v", expected, d)
+		return
+	}
+}
+func TestRequest(t *testing.T) {
+	testRequest(t, Data{
+		SocketProto: tap.SocketProtocol_UDP,
+		SocketFam:   tap.SocketFamily_INET,
+		Address:     net.ParseIP("10.240.0.1"),
+		Port:        40212,
+	}, testingRequest())
+}
+func testingRequest() request.Request {
+	m := new(dns.Msg)
+	m.SetQuestion("example.com.", dns.TypeA)
+	m.SetEdns0(4097, true)
+	return request.Request{W: &test.ResponseWriter{}, Req: m}
+}