tests are failing if you are not running them on a ubuntu box :)

- replaced shell_exec with a more robust Symfony\Component\Process\Process class
- tests failed if you run them on a non-ubuntu box
- tested on ubuntu 13.04 and mac osx 10.8.4


I had to put a little logic in the test... not a good thing but at the moment I think it's the only way to ensure platform compatibility