Fix FSDP destroy process group (#749)

Author: mhuguesaws

3.test_cases/pytorch/FSDP/src/train.py

@@ -275,7 +275,9 @@ def main(args):
           world_size,
           total_steps,
           start_batch_index)
+  
+    dist.destroy_process_group()
 
 if __name__ == "__main__":
     args, _ = parse_args()
-    main(args)
+    main(args)