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 
Can you use expect syntax instead of should? `expect {resource_list.insert(resource)}.to_not raise_error`