Various AWS fixes and shell updates

The first commit should be pretty safe, the second one is a bit more daring, but it needed a rewrite for flexibility, bash independence (it's not installed everywhere) and future expansions.

I did some testing and it should work, however I couldn't get to the end of the salt master deployment on Debian because there are quite a few hardcoded `/root` paths which should be handled through sudo if necessary. I took care of that in the shell script, however it needs to be thought out for the python/fabric part. In this case using the [`sudo()` Fabric operation](http://docs.fabfile.org/en/latest/api/core/operations.html#fabric.operations.sudo) could be a viable solution.