MODULES-1202 - add module_spec_helper support for 3.6 config items

This essentially extends https://github.com/puppetlabs/puppetlabs_spec_helper/pull/65 by also adding support for the "recommended and safe" 3.6 settings ``trusted_node_data``, ``ordering``, and ``stringify_facts``. The first of these is most important to me, as it introduces ``$facts`` and ``$trusted`` as reserved variable names. The former of these is a param name on a define in puppetlabs-mcollective (which now doesn't work on 3.6 with trusted_node_data=true).

This will, AFAIK, need matching work in rspec-puppet. I'll see about getting to work on that.
If you could create similar PRs to rspec-puppet as #209 and comment here, that would be great. I'd rather maintain as little code in puppetlabs_spec_helper as possible if rspec-puppet makes better sense for it (which is pretty much true of all the code in PSH, but that's the eventual goal).