integration: Fix issues reported by the `go vet` tool.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

integration-tests/nghttpx_http1_test.go

@@ -211,7 +211,7 @@ func TestH1H1GracefulShutdown(t *testing.T) {
 	want := io.EOF
 	b := make([]byte, 256)
 	if _, err := st.conn.Read(b); err == nil || err != want {
-		t.Errorf("st.conn.Read(): %v; want %v, %v", err, want)
+		t.Errorf("st.conn.Read(): %v; want %v", err, want)
 	}
 }
 

integration-tests/nghttpx_http2_test.go

@@ -1204,10 +1204,10 @@ func TestH2H1ProxyProtocolV1TCP6(t *testing.T) {
 func TestH2H1ProxyProtocolV1Unknown(t *testing.T) {
 	st := newServerTester([]string{"--accept-proxy-protocol", "--add-x-forwarded-for", "--add-forwarded=for", "--forwarded-for=ip"}, t, func(w http.ResponseWriter, r *http.Request) {
 		if got, notWant := r.Header.Get("X-Forwarded-For"), "192.168.0.2"; got == notWant {
-			t.Errorf("X-Forwarded-For: %v")
+			t.Errorf("X-Forwarded-For: %v; want something else", got)
 		}
 		if got, notWant := r.Header.Get("Forwarded"), "for=192.168.0.2"; got == notWant {
-			t.Errorf("Forwarded: %v")
+			t.Errorf("Forwarded: %v; want something else", got)
 		}
 	})
 	defer st.Close()