install ros into virtualenv

I've made ros install script and test:

1) Create virtualenv venv
2) Install some packages into virtualenv
3) Build ROS and install it under venv/ros
4) Activate venv
5) Activate ros via venv/ros/setup.sh
6) Check that ros and packages installed at step 2 are available
7) Perform same test with --no-index

Hope this will help us to use both ros packages and usual pip packages.