Fixed npm permission errors

npm tried to write into /root/.npm and vagrant up failed with error:
/Stage[langs]/Nodejs/Exec[npm-install]/returns: change from notrun to 0 failed:
/usr/bin/npm install returned 1 instead of one of [0] at
/tmp/vagrant-puppet/manifests/classes/nodejs.pp:21

or similar (/tmp/vagrant-puppet/manifests/classes/statsd.pp:14)