Add riak_test for slf-n_val-sloppy_quorum-options.

Add riak_test for Proxy Get for new options n_val and sloppy_quorum.

See:
https://github.com/basho/riak_kv/pull/553
https://github.com/basho/riak_repl_pb_api/pull/3
https://github.com/basho/riak_repl/pull/302