Adding the support of iTerm2

Hello,

We discussed about it here https://github.com/boot2docker/boot2docker/issues/414
I kept the support of the default terminal, and let the commands at the top so it will be easier to change them if needed.
Working on my laptop so... Try it out too :)
(btw I didn't signed the commit since it's not asked for this repo ;))

ping @SvenDowideit @jlecour