Not exactly "extremely light-weight", but the easiest way to do this would be with docker.
Docker runs on 7.1 out of the box.
Our docker documentation explains how to get it setup and running. Here is that doc http://vlcoredocumentation.readthedocs.org/en/latest/manuals/docker.html
After your docker daemon is up and running, You will need to download this imagehttp://vlcore.vectorlinux.com/pkg/vlbuildslave/docker-images/VL-7.1-BB-FINAL_vlbb-docker.tar.xz
then import it into docker
cat VL-7.1-BB-FINAL_vlbb-docker.tar.xz | docker import - vector:7.1-bb
after that, you can enter the clean build environment as many times as you want
To get a new clean environment:
docker run -ti vector:7.1-bb /bin/bash
if you want to save any of the data from inside that container to the host OS, mount a volume in your docker run command
docker run -ti -v /home/your-docker-work:/data vector:7.1-bb /bin/bash
This will create a bind mount between the host and the docker container. All the data you place in /data will be saved back to the host, that way when you exit the container, the data you want to keep is kept.
see "docker help run" for more, especially, you may want to consider adding the "--rm" argument to docker run for automatic clean up.
THINGS TO REMEMEMBER:
* Everything is disposable in docker, so the data you want to keep you have to bind mount from and to the host (as above)
* You only need to deploy the image once, after that you can create as many containers as you want.
Like I said,
Not exactly "extremely light-weight", but it is as light-weight as it gets in 7.1