net: fix vet warnings

Updates #11041

Change-Id: I12c20beab75d7981efe470eb418e4b58dc8eb066
Reviewed-on: https://go-review.googlesource.com/20002Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/dnsmsg_test.go

@@ -28,7 +28,7 @@ func TestStructPackUnpack(t *testing.T) {
 		t.Fatal("unpacking failed")
 	}
 	if n != len(buf) {
-		t.Error("unpacked different amount than packed: got n = %d, want = %d", n, len(buf))
+		t.Errorf("unpacked different amount than packed: got n = %d, want = %d", n, len(buf))
 	}
 	if !reflect.DeepEqual(got, want) {
 		t.Errorf("got = %+v, want = %+v", got, want)
@@ -69,7 +69,7 @@ func TestDomainNamePackUnpack(t *testing.T) {
 			continue
 		}
 		if n != len(buf) {
-			t.Error(
+			t.Errorf(
 				"unpacked different amount than packed for %s: got n = %d, want = %d",
 				test.in,
 				n,

src/net/http/httptest/server_test.go

@@ -95,6 +95,6 @@ func TestServerCloseClientConnections(t *testing.T) {
 	res, err := http.Get(s.URL)
 	if err == nil {
 		res.Body.Close()
-		t.Fatal("Unexpected response: %#v", res)
+		t.Fatalf("Unexpected response: %#v", res)
 	}
 }

src/net/net_windows_test.go

@@ -561,24 +561,24 @@ func TestInterfaceHardwareAddrWithGetmac(t *testing.T) {
 		if bytes.Contains(line, []byte("Connection Name:")) {
 			f := bytes.Split(line, []byte{':'})
 			if len(f) != 2 {
-				t.Fatal("unexpected \"Connection Name\" line: %q", line)
+				t.Fatalf("unexpected \"Connection Name\" line: %q", line)
 			}
 			name = string(bytes.TrimSpace(f[1]))
 			if name == "" {
-				t.Fatal("empty name on \"Connection Name\" line: %q", line)
+				t.Fatalf("empty name on \"Connection Name\" line: %q", line)
 			}
 		}
 		if bytes.Contains(line, []byte("Physical Address:")) {
 			if name == "" {
-				t.Fatal("no matching name found: %q", string(out))
+				t.Fatalf("no matching name found: %q", string(out))
 			}
 			f := bytes.Split(line, []byte{':'})
 			if len(f) != 2 {
-				t.Fatal("unexpected \"Physical Address\" line: %q", line)
+				t.Fatalf("unexpected \"Physical Address\" line: %q", line)
 			}
 			addr := string(bytes.ToLower(bytes.TrimSpace(f[1])))
 			if addr == "" {
-				t.Fatal("empty address on \"Physical Address\" line: %q", line)
+				t.Fatalf("empty address on \"Physical Address\" line: %q", line)
 			}
 			if addr == "disabled" || addr == "n/a" {
 				continue