update files through puppet-module-skeleton

* add contributing.md, Gemfile and guardfile
* switch Rakefile to parse metadata.json for version
* add nodesets for beaker acceptance tests

n.b.: I've added pry to Gemfile, because it's so very necessary ;)
newparam → newproperty
fix regular expression to actually work

thanks to OnlineCop in #regex

the only problem, calling

   % puppet resource --debug trafficserver_plugin

doesn't return anything :(