Add missing specs for List

* Fixes https://github.com/opscode/chef/issues/2245
* No TODOs to fix.
* Looks like `ResourceCollection` has some internal logic during inserts and it's not super trivial to share examples across classes. In the interest of time I think we should drop the example sharing idea.
* @danielsdeleo is it safe to get rid of json serialization in the ResourceCollection?
* Will add RELEASE_NOTES & CHANGELOG updates before merge.

/cc: @tyler-ball 
The reason I didn't use it is because I wanted to test the `each()` method coded in `ResourceList` class. I don't think each with index is coded. Maybe we can remove [this](https://github.com/opscode/chef/blob/master/lib/chef/resource_collection/resource_list.rb#L74-L78) and [this](https://github.com/opscode/chef/blob/master/lib/chef/resource_collection/resource_list.rb#L88-L96) and delegate `Enumerable.instance_methods` to `@resources` ?