Add protobuf yokozuna admin support

Added Yokozuna admin support and tests for various search queries.

This also requires an installed riak_pb python bundle. For now, you can run `python setup.py install` against the current riak_pb project. This project must be deployed to pypi before this PR can be merged.

In order to run this, you'll need to have `yokozuna = on` in your `riak.conf` file, as well as run the python test with a `RUN_YZ=1` flag. This will activate the yokozuna tests, and deactivate riak search tests. There is no way to run both yokozuna and search tests at the same time, which is fun, since there's no way to run YZ and RS on the same server anyway.