Rubocop fixes and a rubocop config file
Update Ohai plugin for Ohai 7

Pretty big change since this requires Chef 11.12 when using Omnibus
installers.  Prevents warning messages for people using Ohai 7 though
and eventually the Ohai 6 compatibility will go away in Ohai 7
Merge pull request #8 from tas50/master

Update for Ohai 7