added ansible task to add chris-lea ppas for current version nodejs

I added a task to use chris-lea's repos for nodejs.  In other parts of the program, it seems like these repos are preferred to the default ubuntu repos ([see this](https://github.com/edx/edx-platform/blob/master/requirements/system/ubuntu/apt-repos.txt)).  This will keep the nodejs version current as well.

Separately, I fixed a typo where "npm" was listed twice.  Although "nodejs" does not need to be explicitly listed because it is a dependency of npm, I added it for people that may not be familiar with npm.
So doing it this way at least in Ubuntu 12.04 does not work to build edX.  

`The following packages have unmet dependencies:
 nodejs : Conflicts: npm`

I think we should just leave npm in there, not nodejs