[Core] Actor handle refactoring (#8895)

* Marking needed changes.

* Resolve basic dependencies.

* In progress.

* linting.

* In progress 2.

* Linting.

* Refactor done. Cleanup needed.

* Linting.

* Recover kill actor in core worker because it is used inside raylet

* Cleanup.

* Use unique pointer instead. Unit tests are broken now.

* Fix the upstream change.

* Addressed code review 1.

* Lint.

* Addressed code review 2.

* Fix weird github history.

* Lint.

* Linting using clang 7.0.

* Use a better check message.

* Revert cpp stuff.

* Fix weird linting errors.

* Manuall fix all lint issues.

* Update a newline.

* Refactor some interface.

* Addressed all code review.

* Addressed code review

python/ray/util/named_actors.py

@@ -74,7 +74,9 @@ def _register_actor(name, actor_handle):
         exists = False
 
     if exists:
-        raise ValueError("An actor with name={} already exists".format(name))
+        raise ValueError("An actor with name={} already exists or there "
+                         "was timeout in getting this actor handle."
+                         .format(name))
 
     # Add the actor to Redis if it does not already exist.
     _internal_kv_put(actor_name, pickle.dumps(actor_handle), overwrite=True)