Update Riak CS test runner for Riak 2.0

## DO NOT MERGE

Creating this PR for now to allow others to test Riak CS with Riak 2.0. Not sure if this is the approach we want to go with, or if it's even compatible with Riak < 2.0.

@kellymclaughlin @andrewjstone 
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Most of this file has already been copy-pasted from rtdev.erl. We'd like
to eventually fix that, but in the interest of getting the tests
running, this commit just brings it back up to date, using the same
technique.