knife-audit cookbook, chef 11 compatibility

[jhmartin]

https://wiki.opscode.com/display/chef/Breaking+Changes+in+Chef+11 states:

In Chef 10.x and lower, you could see which recipes had been evaluated by chef by looking at node.run_state[:seen_recipes]. Chef::Node was not the correct place to track this information, and the naive implementation resulted in bugs where a recipe "nginx::default" could be loaded after "nginx", even though they're the same recipe.

In the new implementation, this is tracked by Chef::RunContext

So the cookbook should get the list of recipes from:

    node.set["knife_audit"]["seen_recipes"] = run_context.loaded_recipes