YAPF, take 3 (#2098)

* Use pep8 style

The original style file is actually just pep8 style, but with everything
spelled out. It's easier to use the `based_on_style` feature. Any overrides are
clearer that way.

* Improve yapf script

1. Do formatting in parallel
2. Lint RLlib
3. Use .style.yapf file

* Pull out expressions into variables

* Don't format rllib

* Don't allow splits in dicts

* Apply yapf

* Disallow single line if-statements

* Use arithmetic comparison

* Simplify checking for changed files

* Pull out expr into var

python/ray/worker.py

@@ -1558,8 +1558,8 @@ def _init(address_info=None,
         driver_address_info = {
             "node_ip_address": node_ip_address,
             "redis_address": address_info["redis_address"],
-            "store_socket_name":
-            (address_info["object_store_addresses"][0].name),
+            "store_socket_name": (
+                address_info["object_store_addresses"][0].name),
             "webui_url": address_info["webui_url"]
         }
         if not use_raylet: