Some tweaks

* Add the NodeJS PPA when on Ubuntu, otherwise update via NPM
* Use alternatives to create/manage the symlink

This has not (yet) been tested. Please also note that the use of `sudo` will most likely lead to issues in
situations where sudo may ask for a password which cannot be provided by the `salt-minion`. You may want to look for an alternative instead.
Ok, so instead of the PPA `https://deb.nodesource.com/node/dists/` + the GPG key should be added instead. 
Still cleaner than doing an install and upgrading later IMHO :-)