Clean up when a driver disconnects. (#462)

* Clean up state when drivers exit.

* Remove unnecessary field in ActorMapEntry struct.

* Have monitor release GPU resources in Redis when driver exits.

* Enable multiple drivers in multi-node tests and test driver cleanup.

* Make redis GPU allocation a redis transaction and small cleanups.

* Fix multi-node test.

* Small cleanups.

* Make global scheduler take node_ip_address so it appears in the right place in the client table.

* Cleanups.

* Fix linting and cleanups in local scheduler.

* Fix removed_driver_test.

* Fix bug related to vector -> list.

* Fix linting.

* Cleanup.

* Fix multi node tests.

* Fix jenkins tests.

* Add another multi node test with many drivers.

* Fix linting.

* Make the actor creation notification a flatbuffer message.

* Revert "Make the actor creation notification a flatbuffer message."

This reverts commit af99099c8084dbf9177fb4e34c0c9b1a12c78f39.

* Add comment explaining flatbuffer problems.

python/ray/utils.py

@@ -0,0 +1,31 @@
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import binascii
+import sys
+
+import ray.local_scheduler
+
+
+def decode(byte_str):
+  """Make this unicode in Python 3, otherwise leave it as bytes."""
+  if sys.version_info >= (3, 0):
+    return byte_str.decode("ascii")
+  else:
+    return byte_str
+
+
+def binary_to_object_id(binary_object_id):
+  return ray.local_scheduler.ObjectID(binary_object_id)
+
+
+def binary_to_hex(identifier):
+  hex_identifier = binascii.hexlify(identifier)
+  if sys.version_info >= (3, 0):
+    hex_identifier = hex_identifier.decode()
+  return hex_identifier
+
+
+def hex_to_binary(hex_identifier):
+  return binascii.unhexlify(hex_identifier)