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/etcd/group_test.go

@@ -0,0 +1,74 @@
+// +build etcd
+
+package etcd
+
+import (
+	"testing"
+
+	"github.com/coredns/coredns/plugin/etcd/msg"
+	"github.com/coredns/coredns/plugin/pkg/dnsrecorder"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestGroupLookup(t *testing.T) {
+	etc := newEtcdMiddleware()
+
+	for _, serv := range servicesGroup {
+		set(t, etc, serv.Key, 0, serv)
+		defer delete(t, etc, serv.Key)
+	}
+	for _, tc := range dnsTestCasesGroup {
+		m := tc.Msg()
+
+		rec := dnsrecorder.New(&test.ResponseWriter{})
+		_, err := etc.ServeDNS(ctxt, rec, m)
+		if err != nil {
+			t.Errorf("expected no error, got %v\n", err)
+			continue
+		}
+
+		resp := rec.Msg
+		test.SortAndCheck(t, resp, tc)
+	}
+}
+
+// Note the key is encoded as DNS name, while in "reality" it is a etcd path.
+var servicesGroup = []*msg.Service{
+	{Host: "127.0.0.1", Key: "a.dom.skydns.test.", Group: "g1"},
+	{Host: "127.0.0.2", Key: "b.sub.dom.skydns.test.", Group: "g1"},
+
+	{Host: "127.0.0.1", Key: "a.dom2.skydns.test.", Group: "g1"},
+	{Host: "127.0.0.2", Key: "b.sub.dom2.skydns.test.", Group: ""},
+
+	{Host: "127.0.0.1", Key: "a.dom1.skydns.test.", Group: "g1"},
+	{Host: "127.0.0.2", Key: "b.sub.dom1.skydns.test.", Group: "g2"},
+}
+
+var dnsTestCasesGroup = []test.Case{
+	// Groups
+	{
+		// hits the group 'g1' and only includes those records
+		Qname: "dom.skydns.test.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			test.A("dom.skydns.test. 300 IN A 127.0.0.1"),
+			test.A("dom.skydns.test. 300 IN A 127.0.0.2"),
+		},
+	},
+	{
+		// One has group, the other has not...  Include the non-group always.
+		Qname: "dom2.skydns.test.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			test.A("dom2.skydns.test. 300 IN A 127.0.0.1"),
+			test.A("dom2.skydns.test. 300 IN A 127.0.0.2"),
+		},
+	},
+	{
+		// The groups differ.
+		Qname: "dom1.skydns.test.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			test.A("dom1.skydns.test. 300 IN A 127.0.0.1"),
+		},
+	},
+}