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/tune/trainable.py

@@ -203,10 +203,8 @@ class Trainable(object):
         out = io.BytesIO()
         with gzip.GzipFile(fileobj=out, mode="wb") as f:
             compressed = pickle.dumps({
-                "checkpoint_name":
-                os.path.basename(checkpoint_prefix),
-                "data":
-                data,
+                "checkpoint_name": os.path.basename(checkpoint_prefix),
+                "data": data,
             })
             if len(compressed) > 10e6:  # getting pretty large
                 print("Checkpoint size is {} bytes".format(len(compressed)))