Change Node.js executable to be a variable

Node.js executable can be a variable with this change since the actual name of the executable varies with the distribution. Newer Debian distributions - Ubuntu 14.04 LTS uses 'nodejs' instead of 'node'.
Agreed.  For other system requirements, we rely on the executable being in the path (rather than at an absolute path).  Could there be a check for os + `nodejs` in path?  If false, assume `node` in path.