Caching of 'nodejs_latest_version' and 'nodejs_stable_version' facts, should speed up puppetrun and facter

Previously fresh versions were fetched on every puppetrun that seriously slows down my module dev workflow. After caching, fresh versions are fetched once a day and stored in /tmp/puppetfacts/nodejs/cache.yaml . This makes 'time facter -p' roughly 5-6 sec faster (depends on location).

Though not a complete solution to #63, if a cached and recent versions exist, should also avoid problems when nodejs.org is down.

Native caching in Facter will probaly take a long time: https://tickets.puppetlabs.com/browse/FACT-348

Not sure about cache location, appreciate all improvements.