Making tests run in parallel
Add a function to select a free port automatically so the tests can run in parallel.
It would speed up the tests.
It would also ensure that multiple batsim can run in the same machine without collision.
I use to write something to do this, that we can use: https://github.com/oar-team/kameleon/blob/380ca697bad28b120e7df65c6262402f073d8107/contrib/kameleon_bashrc.sh#L208