Stop all application nodes after riak_test run

Updates so that the `riak_test` modules use the `rt_cs_dev` test harness instead
of the `rtdev` Riak harness. This has changes to properly stop all of the CS and
Stanchion nodes. It also requires some configuration changes. See the updates
to the `README` in the `riak_test` subdirectory for more details.

This PR relies on [this](https://github.com/basho/riak_test/pull/297) PR introducing the RiakCS test harness for `riak_test`.