warn users when checkpoint save fails (#879)

Summary:
Pull Request resolved: #879

ATTS

Reviewed By: diego-urgell

Differential Revision: D61165902

fbshipit-source-id: 895a2814ff4c12f2afb0f61ee0794a52740aec8e

Author: anshulverma

torchtnt/framework/callbacks/dcp_saver.py

@@ -242,7 +242,10 @@ def _save(
                 storage_writer=storage_writer,
                 planner=planner,
             )
-        except AttributeError:
+        except AttributeError as ex:
+            logger.warning(
+                f"Unable to save checkpoint (will retry saving using deprecated API). Error: {ex}"
+            )
             dcp.save_state_dict(
                 state_dict={"app_state": MultiStateful(app_state)},
                 process_group=self._process_group,