After discussion with Helin and Yi, this change adds "print_operators_doc" executable to the Paddle docker nightly image.  This docker image will be pulled by PaddlePaddle.org nightly job and will generate the operator documentation to be put on PaddlePaddle.org website.

* init add

* add topk op

* someupdate

* fix style check

* add test py file

* update top k cuda kernel

* follow comments

* remove debug print

* fix casting error

* fix casting error

* fix casting error

* fix rename bug...

* fix travis

Fix invalid paddle executable file path with pip install  

Otherwise the production image generation will fail due to deb not
found, or executable built from Go not found.

Fix C-API Compilation Error

* User must install Paddle python package before unittest.
* Or use docker to build Paddle

* Do not use `virtualenv` in Docker
* Split unittest into many target, make them parallel

* using etcd as fault tolerant training

* update

* workable version, ft not tested

* small fix

* update

* remove TODO