Fix pipline dataloader when batch elements contain tuple (#565)

Co-authored-by: NJeff Rasley <jerasley@microsoft.com>
Co-authored-by: NAmmar Ahmad Awan <ammar.awan@microsoft.com>

deepspeed/runtime/pipe/engine.py

@@ -795,7 +795,8 @@ class PipelineEngine(DeepSpeedEngine):
             loaded = batch[1]
             if torch.is_tensor(batch[1]):
                 loaded = batch[1].to(self.device)
-            elif isinstance(batch[1], tuple):
+            # XXX: torch 1.6.0 DataLoader will auto convert tuple to list
+            elif isinstance(batch[1], (tuple, list)):
                 loaded = []
                 for x in batch[1]:
                     assert torch.is_tensor(x)