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/reverse/reverse_test.go

@@ -0,0 +1,71 @@
+package reverse
+
+import (
+	"net"
+	"regexp"
+	"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 TestReverse(t *testing.T) {
+	_, net4, _ := net.ParseCIDR("10.1.1.0/24")
+	regexIP4, _ := regexp.Compile("^.*ip-" + regexMatchV4 + "\\.example\\.org\\.$")
+
+	em := Reverse{
+		Networks: networks{network{
+			IPnet:        net4,
+			Zone:         "example.org",
+			Template:     "ip-{ip}.example.org.",
+			RegexMatchIP: regexIP4,
+		}},
+		Fallthrough: false,
+	}
+
+	tests := []struct {
+		next          plugin.Handler
+		qname         string
+		qtype         uint16
+		expectedCode  int
+		expectedReply string
+		expectedErr   error
+	}{
+		{
+			next:          test.NextHandler(dns.RcodeSuccess, nil),
+			qname:         "test.ip-10.1.1.2.example.org",
+			expectedCode:  dns.RcodeSuccess,
+			expectedReply: "10.1.1.2",
+			expectedErr:   nil,
+		},
+	}
+
+	ctx := context.TODO()
+
+	for i, tr := range tests {
+		req := new(dns.Msg)
+
+		tr.qtype = dns.TypeA
+		req.SetQuestion(dns.Fqdn(tr.qname), tr.qtype)
+
+		rec := dnsrecorder.New(&test.ResponseWriter{})
+		code, err := em.ServeDNS(ctx, rec, req)
+
+		if err != tr.expectedErr {
+			t.Errorf("Test %d: Expected error %v, but got %v", i, tr.expectedErr, err)
+		}
+		if code != int(tr.expectedCode) {
+			t.Errorf("Test %d: Expected status code %d, but got %d", i, tr.expectedCode, code)
+		}
+		if tr.expectedReply != "" {
+			answer := rec.Msg.Answer[0].(*dns.A).A.String()
+			if answer != tr.expectedReply {
+				t.Errorf("Test %d: Expected answer %s, but got %s", i, tr.expectedReply, answer)
+			}
+		}
+	}
+}