Adding support for ChefSpec platform family

When running tests with ChefSpec I load the build-essentials recipe and a number of warnings appear stating that the node's platform is not supported. The node is the chefspec generated node from Fauxhai.

The node currently does not have a platform family. It is set to nil with ChefSpec 4.0.1 version. I have proposed a pull request to set the platform_family to `chefspec` for a ChefSpec node. This pull request would support the platform family so that tests do not generate a lot of extraneous error messages.