Added support for keras estimator

horovod/spark/keras/estimator.py

@@ -14,7 +14,7 @@
 # ==============================================================================
 import numbers
 import time
-
+import os
 import numpy as np
 import tensorflow as tf
 
@@ -282,7 +282,10 @@ def _fit_on_prepared_data(self, backend, train_rows, val_rows, metadata, avg_row
 
     def _load_model_from_checkpoint(self, run_id):
         store = self.getStore()
-        last_ckpt_path = store.get_checkpoint_path(run_id)
+        last_ckpt_path = os.path.join(store.get_checkpoint_path(run_id), store.get_checkpoint_filename())
+
+        if not store.fs.exists(last_ckpt_path):
+            return None
 
         if self.getVerbose():
             print('Resuming training from last checkpoint: {}'.format(last_ckpt_path))