Make entity_uuid work for Chef Infra 15

[alexpop]

Fixes #368

[lamont-granquist]

I dunno maybe it doesn't matter but this module gets included in a lot of different contexts where it looks like there my be no node object so that will blow up. It seems to be used off of a run_status which seems to be the actual Chef::RunStatus object? I don't understand how the wiring happens there. It does inject itself into the Chef::Recipe DSL, but that shouldn't appear in the RunStatus object which inherits from nothing and AFAIK nothing gets mixed into it.

So.... this might work, but there still may be a pile of software developer footguns left lying around on the floor here...

This also clearly broke, but no tests went red. That indicates that there really needs to be a test.

[alexpop]

I would like to see a refactoring on how the node guid is identified.
For now, let's get this in to unblock Chef Infra 15 users. Travis tests are passing and I also manually tested it with the chef-automate reporter.