[Distributed Example] Check args.num_servers with DGL_NUM_SERVER (#2203)

* update

* update

* update

examples/pytorch/graphsage/experimental/train_dist.py

@@ -316,7 +316,9 @@ if __name__ == '__main__':
     parser.add_argument('--close_profiler', action='store_true', help='Close pyinstrument profiler')
     args = parser.parse_args()
     assert args.num_workers == int(os.environ.get('DGL_NUM_SAMPLER')), \
-    'The num_workers should be the same value with num_samplers.'
+    'The num_workers should be the same value with DGL_NUM_SAMPLER.'
+    assert args.num_servers == int(os.environ.get('DGL_NUM_SERVER')), \
+    'The num_servers should be the same value with DGL_NUM_SERVER.'
 
     print(args)
     main(args)

examples/pytorch/graphsage/experimental/train_dist_unsupervised.py

@@ -486,7 +486,9 @@ if __name__ == '__main__':
         help="whether to remove edges during sampling")
     args = parser.parse_args()
     assert args.num_workers == int(os.environ.get('DGL_NUM_SAMPLER')), \
-    'The num_workers should be the same value with num_samplers.'
-
+    'The num_workers should be the same value with DGL_NUM_SAMPLER.'
+    assert args.num_servers == int(os.environ.get('DGL_NUM_SERVER')), \
+    'The num_servers should be the same value with DGL_NUM_SERVER.'
+    
     print(args)
     main(args)