Fix the interface to each AB test in alpha-comm

The AB test run(context, config) interface changed yesterday (b4520afd0182d434e8ae49705b3a664875191569), which half broke our alpha-comm test when it was merged in to master as it was already using the second parameter internally for something else.

The alpha-comm code shouldn't have been doing that really.

/cc @rich-nguyen Oops.

```
$ git diff b09c774..HEAD app/assets/javascripts/modules/experiments/ab.js

@@ -127,7 +115,7 @@ define([
             variantId = participations[test.id].variant;
             test.variants.some(function(variant) {
                 if (variant.id === variantId) {
-                    variant.test(context);
+                    variant.test(context, config);
                     return true;
                 }
```