Changes to local scheduler client protocol. (#435)

* Make local scheduler clients receive reply upon registration.

* Fix tests and linting.

python/ray/local_scheduler/test/test.py

@@ -16,6 +16,7 @@ import ray.plasma as plasma
 USE_VALGRIND = False
 ID_SIZE = 20
 
+NIL_WORKER_ID = 20 * b"\xff"
 NIL_ACTOR_ID = 20 * b"\xff"
 
 
@@ -47,7 +48,7 @@ class TestLocalSchedulerClient(unittest.TestCase):
         plasma_store_name, use_valgrind=USE_VALGRIND)
     # Connect to the scheduler.
     self.local_scheduler_client = local_scheduler.LocalSchedulerClient(
-        scheduler_name, NIL_ACTOR_ID, False)
+        scheduler_name, NIL_WORKER_ID, NIL_ACTOR_ID, False)
 
   def tearDown(self):
     # Check that the processes are still alive.