apputils/checkpoint.py - relax requirements when loading thinned models

Allow loading a thinned model from a checkpoint file that doesn't
contain a CompressionSchedule.  After thinning, we usually don't have,
or care about, a pruning schedule - so we don't need to force the
user to create one, just for saving in the checkpoint.

distiller/apputils/checkpoint.py

@@ -147,7 +147,8 @@ def load_checkpoint(model, chkpt_file, optimizer=None, model_device=None, *,
 
     if 'thinning_recipes' in checkpoint:
         if 'compression_sched' not in checkpoint:
-            raise KeyError("Found thinning_recipes key, but missing mandatory key compression_sched")
+            msglogger.warning("Found thinning_recipes key, but missing mandatory key compression_sched")
+            compression_scheduler = distiller.CompressionScheduler(model)
         msglogger.info("Loaded a thinning recipe from the checkpoint")
         # Cache the recipes in case we need them later
         model.thinning_recipes = checkpoint['thinning_recipes']