Provide consistent experience of status code in api description when an action returns a DTO vs void

**Current Behavior**
For this action an apidescription would have status code information as 200 OK

``` c#
public Product Get()
```

For this action we do NOT provide a response type description(which contains status code info)

``` c#
public void DoSomething()
```

From here:
https://github.com/aspnet/Mvc/pull/4831#discussion_r66485808

cc @rynowak 
