First pass at DSL additions for chef-client audit mode

@mcquin @sersut 
```ruby
controls "mysql audit" do
  control service('mysql') do
    ...
  end
end
```

If you have that code in your recipe, I am passing the outer-most block as an `ExampleGroup` instance to the runner.  It seemed like this made a lot more sense than trying to have both a `controls` and `control` DSL method.

It also allows you to use other rspec methods outside the scope of each `control` block, like a `let`:

```ruby
controls "foo" do
  let(:bar) { "bar" }
end
```