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.
Refactored nodejs formula
Merge pull request #4 from syphernl/refactored

Refactored nodejs formula