* [CodeStyle][E711] use `is`/`is not` for comparison with `None`

* `self.assertTrue($A is None)` -> `self.assertIsNone($A)`

* `self.assertTrue($A is not None)` -> `self.assertIsNotNone($A)`

* `self.assertFalse($A is None)` -> `self.assertIsNotNone($A)`

* `self.assertEqual($A, None)` -> `self.assertIsNone($A)`

* `self.assertNotEqual($A, None)` -> `self.assertIsNotNone($A)`

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* add reducer

* refine envent for memorycopy

* add concat&split for allreduce

* apply concat & split for fuse tensor

* fix nccl dep

* fix the untest, compile problem and ddp initialize problem

* fix untest for mac & add some comments & solve the repeated param in sublayers

* fix untest for windows & fix document

* raise error if use multi-cards in fleet non_distributed mode; test=develop

* fleet support non_distributed training in dygraph mode; test=develop

* add get final strategy for user to print final strategy

* test=develop, bug fix

* fix fleet util and gloo

* fix worker endpoints

* fix

* fix UT

* fix gloo

* fix gloo

* update gloo

* update gloo

* update gloo

* update gloo

* update gloo

* fix gloo wrapper for hdfs

* add file gloo and UT

* fix UT

* fix UT

* fix UT

* hide public method of RoleMaker

* fix UT

* GPU fleetrun support gloo

* parameterserver fleetrun support gloo

* add UT

* add UT

* fix UT

* fix get server endpoint

* fix get server endpoint

* fix UT

* hide public method of rolemaker

* hide public method of rolemaker

* hide public method of rolemaker

* Update test_fleet_rolemaker_new.py

* hide public method of rolemaker

* hide public method of rolemaker

* fix worker endpoints

* fix gloo wrapper for hdfs

* GPU fleetrun support gloo

* parameterserver fleetrun support gloo

* fix get server endpoint

paddle.distributed.fleet supports dynamic graph execution.

* support running python train.py for fleet-task; test=develop

* add save/load for parameter server

* add feature to fleet2.0 role_maker, distribute_strategy, test=develop

* set default value to strategy in distributed_optimizer test=develop

* move paddle.fleet to paddle.distributed.fleet

refactor fleet api under paddle.fleet
update DistributedStrategy