net/http, net/http/httputil: fix nits found by vet

Change-Id: Idf02428591f61dc58f654fdaf0e3a55f8b8a1060
Reviewed-on: https://go-review.googlesource.com/18350Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/httputil/reverseproxy_test.go

@@ -392,7 +392,7 @@ func TestReverseProxy_Post(t *testing.T) {
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		slurp, err := ioutil.ReadAll(r.Body)
 		if err != nil {
-			t.Error("Backend body read = %v", err)
+			t.Errorf("Backend body read = %v", err)
 		}
 		if len(slurp) != len(requestBody) {
 			t.Errorf("Backend read %d request body bytes; want %d", len(slurp), len(requestBody))

src/net/http/serve_test.go

@@ -1077,7 +1077,7 @@ Try:
 		}
 	}
 	if !ok {
-		t.Fatal("Failed to start up after %d tries", maxTries)
+		t.Fatalf("Failed to start up after %d tries", maxTries)
 	}
 	defer ln.Close()
 	c, err := tls.Dial("tcp", ln.Addr().String(), &tls.Config{
@@ -2496,7 +2496,7 @@ func TestHijackBeforeRequestBodyRead(t *testing.T) {
 		gone := w.(CloseNotifier).CloseNotify()
 		slurp, err := ioutil.ReadAll(reqBody)
 		if err != nil {
-			t.Error("Body read: %v", err)
+			t.Errorf("Body read: %v", err)
 			return
 		}
 		if len(slurp) != len(requestBody) {