Update paver bok_choy (test) commands to reflect new default vars.

@clytwynec @nasthagiri 

This takes into account recent changes for how bok-choy commands are composed in paver. (Should also bring Jenkins back to green.)


@nasthagiri how important is the redline message saying "we're going to use split as the default_store"?

Sorry about the confusion; I actually hadn't looked that much at acceptance_test.py so my view would be bok_choy-centric here. I see the change you're suggesting, @clytwynec and was looking at that. I think it could work although I haven't 100% vetted it out.