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/chaos/chaos_test.go

@@ -0,0 +1,80 @@
+package chaos
+
+import (
+	"testing"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnsrecorder"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+func TestChaos(t *testing.T) {
+	em := Chaos{
+		Version: version,
+		Authors: map[string]bool{"Miek Gieben": true},
+	}
+
+	tests := []struct {
+		next          plugin.Handler
+		qname         string
+		qtype         uint16
+		expectedCode  int
+		expectedReply string
+		expectedErr   error
+	}{
+		{
+			next:          test.NextHandler(dns.RcodeSuccess, nil),
+			qname:         "version.bind",
+			expectedCode:  dns.RcodeSuccess,
+			expectedReply: version,
+			expectedErr:   nil,
+		},
+		{
+			next:          test.NextHandler(dns.RcodeSuccess, nil),
+			qname:         "authors.bind",
+			expectedCode:  dns.RcodeSuccess,
+			expectedReply: "Miek Gieben",
+			expectedErr:   nil,
+		},
+		{
+			next:         test.NextHandler(dns.RcodeSuccess, nil),
+			qname:        "authors.bind",
+			qtype:        dns.TypeSRV,
+			expectedCode: dns.RcodeSuccess,
+			expectedErr:  nil,
+		},
+	}
+
+	ctx := context.TODO()
+
+	for i, tc := range tests {
+		req := new(dns.Msg)
+		if tc.qtype == 0 {
+			tc.qtype = dns.TypeTXT
+		}
+		req.SetQuestion(dns.Fqdn(tc.qname), tc.qtype)
+		req.Question[0].Qclass = dns.ClassCHAOS
+		em.Next = tc.next
+
+		rec := dnsrecorder.New(&test.ResponseWriter{})
+		code, err := em.ServeDNS(ctx, rec, req)
+
+		if err != tc.expectedErr {
+			t.Errorf("Test %d: Expected error %v, but got %v", i, tc.expectedErr, err)
+		}
+		if code != int(tc.expectedCode) {
+			t.Errorf("Test %d: Expected status code %d, but got %d", i, tc.expectedCode, code)
+		}
+		if tc.expectedReply != "" {
+			answer := rec.Msg.Answer[0].(*dns.TXT).Txt[0]
+			if answer != tc.expectedReply {
+				t.Errorf("Test %d: Expected answer %s, but got %s", i, tc.expectedReply, answer)
+			}
+		}
+	}
+}
+
+const version = "CoreDNS-001"