[rllib] Remove need to pass around registry (#2250)

* remove registry

* fix

* too many _

* fix

* cloudpickle

* Update registry.py

* yapf

* fix test

* fix kv check

python/ray/experimental/internal_kv.py

@@ -0,0 +1,31 @@
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import ray
+
+
+def _internal_kv_initialized():
+    worker = ray.worker.get_global_worker()
+    return hasattr(worker, "mode") and worker.mode is not None
+
+
+def _internal_kv_get(key):
+    """Fetch the value of a binary key."""
+
+    worker = ray.worker.get_global_worker()
+    return worker.redis_client.hget(key, "value")
+
+
+def _internal_kv_put(key, value):
+    """Globally associates a value with a given binary key.
+
+    This only has an effect if the key does not already have a value.
+
+    Returns
+        already_exists (bool): whether the value already exists.
+    """
+
+    worker = ray.worker.get_global_worker()
+    updated = worker.redis_client.hsetnx(key, "value", value)
+    return updated == 0  # already exists