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/autoscaler/aws/node_provider.py

@@ -101,12 +101,9 @@ class AWSNodeProvider(NodeProvider):
                 "Value": v,
             })
         conf.update({
-            "MinCount":
-            1,
-            "MaxCount":
-            count,
-            "TagSpecifications":
-            conf.get("TagSpecifications", []) + [{
+            "MinCount": 1,
+            "MaxCount": count,
+            "TagSpecifications": conf.get("TagSpecifications", []) + [{
                 "ResourceType": "instance",
                 "Tags": tag_pairs,
             }]