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/dnssec/cache_test.go

@@ -0,0 +1,34 @@
+package dnssec
+
+import (
+	"testing"
+	"time"
+
+	"github.com/coredns/coredns/plugin/pkg/cache"
+	"github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/request"
+)
+
+func TestCacheSet(t *testing.T) {
+	fPriv, rmPriv, _ := test.TempFile(".", privKey)
+	fPub, rmPub, _ := test.TempFile(".", pubKey)
+	defer rmPriv()
+	defer rmPub()
+
+	dnskey, err := ParseKeyFile(fPub, fPriv)
+	if err != nil {
+		t.Fatalf("failed to parse key: %v\n", err)
+	}
+
+	c := cache.New(defaultCap)
+	m := testMsg()
+	state := request.Request{Req: m}
+	k := hash(m.Answer) // calculate *before* we add the sig
+	d := New([]string{"miek.nl."}, []*DNSKEY{dnskey}, nil, c)
+	d.Sign(state, "miek.nl.", time.Now().UTC())
+
+	_, ok := d.get(k)
+	if !ok {
+		t.Errorf("signature was not added to the cache")
+	}
+}