Ohai 7 Compatibility for Chef

This PR makes Chef compatible with Ohai 7. 

Plan of Record is to ship ohai-7 branch as a pre-release gem in order to enable test runs for OHAI 7. 

Note that this branch is based on 11.8.2.

@danielsdeleo anything I'm missing?
/cc: @mcquin / @lamont-granquist