Chef 13 Upgrade: Lessons Learnt and Documented for Posterity

I've recently been working through upgrading my Chef 12 cookbooks to Chef 13, as Chef 12 is to be End of Life'd in April 2018.

As part of this, there have been a few snags I've hit with respect to Chef 13 + Rubocop and Chef 13 + ChefSpec within my existing cookbooks.

For reasons I won't go into, I'm still using Rubocop over the Chef-recommended CookStyle, which it seems would have resolved a few of these issues.

Note that some, but not all, of the Rubocop fixes can be automagically resolved using rubocop --auto-correct.