Support for Riak 2.0

This pull request attempts to resolve https://github.com/basho/riak-chef-cookbook/issues/94.

In addition to Riak 2.0 support, the following issues have been addressed:

- https://github.com/basho/riak-chef-cookbook/issues/51
- https://github.com/basho/riak-chef-cookbook/issues/105
- https://github.com/basho/riak-chef-cookbook/issues/106