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.

test/jenkins_tests/multi_node_tests/test_0.py

@@ -15,7 +15,11 @@ def f():
 
 
 if __name__ == "__main__":
-  ray.init(redis_address=os.environ["RAY_REDIS_ADDRESS"])
+  driver_index = int(os.environ["RAY_DRIVER_INDEX"])
+  redis_address = os.environ["RAY_REDIS_ADDRESS"]
+  print("Driver {} started at {}.".format(driver_index, time.time()))
+
+  ray.init(redis_address=redis_address)
   # Check that tasks are scheduled on all nodes.
   num_attempts = 30
   for i in range(num_attempts):
@@ -26,3 +30,5 @@ if __name__ == "__main__":
     if len(counts) == 5:
       break
   assert len(counts) == 5
+
+  print("Driver {} finished at {}.".format(driver_index, time.time()))