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/kubernetes/kubernetes_apex_test.go

@@ -0,0 +1,68 @@
+package kubernetes
+
+import (
+	"testing"
+
+	"github.com/coredns/coredns/plugin/pkg/dnsrecorder"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+var kubeApexCases = [](test.Case){
+	{
+		Qname: "cluster.local.", Qtype: dns.TypeSOA,
+		Rcode: dns.RcodeSuccess,
+		Answer: []dns.RR{
+			test.SOA("cluster.local.	303	IN	SOA	ns.dns.cluster.local. hostmaster.cluster.local. 1499347823 7200 1800 86400 60"),
+		},
+	},
+	{
+		Qname: "cluster.local.", Qtype: dns.TypeHINFO,
+		Rcode: dns.RcodeSuccess,
+		Ns: []dns.RR{
+			test.SOA("cluster.local.	303	IN	SOA	ns.dns.cluster.local. hostmaster.cluster.local. 1499347823 7200 1800 86400 60"),
+		},
+	},
+	{
+		Qname: "cluster.local.", Qtype: dns.TypeNS,
+		Rcode: dns.RcodeSuccess,
+		Answer: []dns.RR{
+			test.NS("cluster.local. 303     IN      NS     ns.dns.cluster.local."),
+		},
+		Extra: []dns.RR{
+			test.A("ns.dns.cluster.local.   303       IN      A       127.0.0.1"),
+		},
+	},
+}
+
+func TestServeDNSApex(t *testing.T) {
+
+	k := New([]string{"cluster.local."})
+	k.APIConn = &APIConnServeTest{}
+	k.Next = test.NextHandler(dns.RcodeSuccess, nil)
+	ctx := context.TODO()
+
+	for i, tc := range kubeApexCases {
+		r := tc.Msg()
+
+		w := dnsrecorder.New(&test.ResponseWriter{})
+
+		_, err := k.ServeDNS(ctx, w, r)
+		if err != tc.Error {
+			t.Errorf("Test %d, expected no error, got %v\n", i, err)
+			return
+		}
+		if tc.Error != nil {
+			continue
+		}
+
+		resp := w.Msg
+		if resp == nil {
+			t.Fatalf("Test %d, got nil message and no error ford", i)
+		}
+
+		test.SortAndCheck(t, resp, tc)
+	}
+}