[PAI bug fixing] Fix the incorrect PAI webhdfs endpoint path (#653)

* Fix PAI webhdfs api endpoint

src/nni_manager/training_service/pai/paiTrainingService.ts

@@ -356,7 +356,7 @@ class PAITrainingService implements TrainingService {
                     user: this.paiClusterConfig.userName,
                     // Refer PAI document for Pylon mapping https://github.com/Microsoft/pai/tree/master/docs/pylon
                     port: 80,
-                    path: '/webhdfs/webhdfs/v1',
+                    path: '/webhdfs/api/v1',
                     host: this.paiClusterConfig.host
                 });