Recover the mistakenly deleted WARPCTC variable in cmake.

* 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

* Also, test_plot cannot run in MacOS because of matplotlib & ipython's
  limit.
* Add missing dependency in setup.py.
* fix #2264

When using system python, "pip install" needs root previlege. Using virtualenv to avoid this.

In the original util.cmake. enable_virtualenv.c is always regenerated when cmake files are changed, which leads to the relinking of all the targets depends on paddle_utils.

* See [here](https://gflags.github.io/gflags/#cmake).

The resource "unsigned char[]" array generated by create_source needs to have 0 ending as a valid C string to be used in PythonUtil.cpp initPython()

Change-Id: I5e214606ed9102f37813ea3f07565dc10a9c015e

* add rdma cmake support

* move rdma related code to rdma.cmake

* Fix bug in yield dictionary in DataProvider.
* Also make virtualenv work in Paddle.

* follow comments to fix bugs

* Also fix a bug, we should link -ldl at last