[tune] Stop-gap fix for PBT checkpointing (#7794)

* Fix PBT

* lint

* reset

* rm

* tests

Co-authored-by: Richard Liaw <rliaw@berkeley.edu>

python/ray/tune/trainable.py

@@ -186,7 +186,7 @@ class Trainable:
     def default_resource_request(cls, config):
         """Provides a static resource requirement for the given configuration.
 
-        This can be overriden by sub-classes to set the correct trial resource
+        This can be overridden by sub-classes to set the correct trial resource
         allocation, so the user does not need to.
 
         .. code-block:: python
@@ -555,6 +555,16 @@ class Trainable:
         """
         return self._iteration
 
+    @property
+    def training_iteration(self):
+        """Current training iteration (same as `self.iteration`).
+
+        This value is automatically incremented every time `train()` is called
+        and is automatically inserted into the training result dict.
+
+        """
+        return self._iteration
+
     def get_config(self):
         """Returns configuration passed in by Tune."""
         return self.config