Ability to change the associated group configuration for a split test

STUD-1658

My sandbox has the latest version of this PR.
http://studio.cahrens.m.sandbox.edx.org/
This was a mistake that I already removed but didn't push up yet. I started playing with putting the test here, but then decided to go ahead and create a cms.runtime.v1_spec.js to house all the runtime tests.