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

This only fixes the issue for ATLAS
MKL is still another fix.

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.

It seems that is not used.

* When SWIG_PY is not enabled, paddle.v2 package cannot be used.
* When PYTHON is not enabled, PyDataProvider cannot be used.

Fix issue #1920

* When SWIG_PY is not enabled, paddle.v2 package cannot be used.
* When PYTHON is not enabled, PyDataProvider cannot be used.

Fix issue #1920

Change-Id: Ia29cd3d205e401dc3d04fbaf3cba2b01f2f4f0ca

* Fix #1877

Currently, Paddle only support Python use the sample version of
Protobuf that CPP do.