Remove the pserver, trainer, evaluators and some useless gradientmachines when compile mobile inference library.

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).