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

* Also make use cmake find to zlib.
* circle link in osx, use reverse link all libs instead. But
  maybe osx just don't care circle link.

ISSUE=4586495

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1408 1ad973e4-5ce8-4261-8a94-b56d1f490c56