clientv3/integration: Fix flaky TestGetTokenWithoutAuth (#12200)

The test is vary flaky on Travis.

Seems that since (#7724) the
client is expected to simply ignore whether server is in AuthDisabled
mode even if the user supplies credentials.

The tests used to:
  * use very large cluster (10 nodes)
  * set very low timeout (1 sec)

Such setup led to frequent deadlineExceed errors or following failures:

    === RUN   TestGetTokenWithoutAuth
    {"level":"warn","ts":"2020-08-04T16:50:48.686+0200","caller":"clientv3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"endpoint://client-35573307-1ee5-441b-acc7-d073f0bd7de5/localhost:69820396562031027440","attempt":0,"error":"rpc error: code = Unavailable desc = etcdserver: leader changed"}
        user_test.go:151: other errors:etcdserver: leader changed
    --- FAIL: TestGetTokenWithoutAuth (10.91s)

clientv3/client.go

@@ -337,7 +337,13 @@ func (c *Client) dial(target string, creds grpccredentials.TransportCredentials,
 
 		err = c.getToken(ctx)
 		if err != nil {
+			// TODO: Consider retrying transient errors like:
+			// "error":"rpc error: code = Unavailable desc = etcdserver: leader changed"
+
+			// Ignore rpctypes.ErrAuthNotEnabled error.
 			if toErr(ctx, err) != rpctypes.ErrAuthNotEnabled {
+				// This logic originates from 62d7bae496 and is not clear why we cannot just return err
+				// without looking into parent's context.
 				if err == ctx.Err() && ctx.Err() != c.ctx.Err() {
 					err = context.DeadlineExceeded
 				}

clientv3/integration/user_test.go

@@ -111,10 +111,11 @@ func authSetupRoot(t *testing.T, auth clientv3.Auth) {
 	}
 }
 
+// Client can connect to etcd even if they supply credentials and the server is in AuthDisable mode.
 func TestGetTokenWithoutAuth(t *testing.T) {
 	defer testutil.AfterTest(t)
 
-	clus := integration.NewClusterV3(t, &integration.ClusterConfig{Size: 10})
+	clus := integration.NewClusterV3(t, &integration.ClusterConfig{Size: 2})
 	defer clus.Terminate(t)
 
 	authapi := clus.RandClient()
@@ -130,7 +131,7 @@ func TestGetTokenWithoutAuth(t *testing.T) {
 	// "Username" and "Password" must be used
 	cfg := clientv3.Config{
 		Endpoints:   authapi.Endpoints(),
-		DialTimeout: 1 * time.Second, // make sure all connection time of connect all endpoint must be more DialTimeout
+		DialTimeout: 5 * time.Second,
 		Username:    "root",
 		Password:    "123",
 	}
@@ -142,13 +143,10 @@ func TestGetTokenWithoutAuth(t *testing.T) {
 
 	switch err {
 	case nil:
-		t.Log("passes as expected, but may be connection time less than DialTimeout")
+		t.Log("passes as expected")
 	case context.DeadlineExceeded:
 		t.Errorf("not expected result:%v with endpoint:%s", err, authapi.Endpoints())
-	case rpctypes.ErrAuthNotEnabled:
-		t.Logf("passes as expected:%v", err)
 	default:
 		t.Errorf("other errors:%v", err)
 	}
-
 }