Bump Riak and Riak CS cookbooks (default to Riak CS 1.4.3)

In addition to bumping the cookbook version:

- [x] Set Riak's `pb_backlog` to the same as `request_pool` for Riak CS (resolves #31)
- [x] Set `fold_objects_for_list_keys` to `true` (requires Riak 1.4+)