[webappsec-testsuite] runner.js puzzler

So, I've made some fixes to reporting to accommodate Firefox not accepting
cookies on CSP reports, but now I'm noticing something else strange: It's
only running half the tests.

After a bit of debugging, it seems that runner.js is using completion
callbacks from testharness.js to advance through the manifest.  The CSP
cases all have an sub-iframe for checking the report, and callbacks are
bubbling up from that and causing the runner to advance prematurely, so
every other test gets skipped. (at least that's what I think is happening)

But only in Firefox!  ¯\(°_o)/¯

Anyone have any ideas?

-Brad