* Fix bug of reduce_sum op. When input.numel() > INT32_MAX, its result
is wrong.

* Remove climits.

* Clean fluid API in paddle/distributed and paddle/fleetx folders.
Include following files:
python/paddle/distributed/__init__.py
python/paddle/distributed/collective.py
python/paddle/distributed/fleet/utils/fs.py
python/paddle/distributed/fleet/utils/hybrid_parallel_inference.py
python/paddle/distributed/fleet/utils/hybrid_parallel_util.py
python/paddle/distributed/fleet/utils/internal_storage.py
python/paddle/distributed/launch/context/device.py
python/paddle/distributed/parallel.py
python/paddle/distributed/parallel_with_gloo.py
python/paddle/distributed/spawn.py
python/paddle/framework/__init__.py
To be mentioned, 'paddle.fluid.dygraph.parallel.ParallelEnv'
 and 'fluid.framework.core' keeps unchanged in those files.
ParallelEnv is used by paddle.fluid.dygraph.parallel.DataParallel.
However, APIs in paddle.fluid.dygraph.parallel can't be
migrated to paddle.distributed, as there exists cyclic import
dependencies in modules like paddle.static, paddle.tensor. And
'fluid.framework.core' will be changed to import framework.core
after fluid.core is transmitted.

* Change TODO authors.

* isort all files

* revert conflicting files

* revert conflicting files

* revert conflicting files

* [CodeStyle][py2][U004] unecessary explicit `object` inheritance in class definition

* fix an increment

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* make launch compatible

* fix ut

* fix log offset

* [CustomDevice] add custom ccl 2/2

* update

* update

* update launch

* update paddle.distributed.launch

* add sample code

* update shell

* fix typo

* fix typo

* update docs

* rm code

* fix doc 2

* fix doc 3

* fix doc 4
Co-authored-by: Nroot <root@sgjur-pod004-1.ipu.graphcore.cn>

* 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

This reverts commit e680d581.

* [IPU] support paddle.distributed.launch with IPUs

* add device_num to env_args_mapping