middleware->plugin renaming (#1161)

These file still had middleware in their name, rename to plugin.

test/plugin_test.go

@@ -0,0 +1,43 @@
+package test
+
+import (
+	"io/ioutil"
+	"log"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func benchmarkLookupBalanceRewriteCache(b *testing.B) {
+	t := new(testing.T)
+	name, rm, err := test.TempFile(".", exampleOrg)
+	if err != nil {
+		t.Fatalf("failed to create zone: %s", err)
+	}
+	defer rm()
+
+	corefile := `example.org:0 {
+    file ` + name + `
+    rewrite type ANY HINFO
+    loadbalance
+}
+`
+
+	ex, udp, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	defer ex.Stop()
+
+	log.SetOutput(ioutil.Discard)
+	c := new(dns.Client)
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeA)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		c.Exchange(m, udp)
+	}
+}