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.)


Sure, that makes sense.  We chose to do it this way in the split/paver PR, since it was consistent with the defaults set in [acceptance_test.py](https://github.com/edx/edx-platform/blob/master/pavelib/acceptance_test.py#L41).  However, as you point out, it's not internally consistent with how it is done for other bokchoy defaults.