Add & fix interaction_data tests.

* Fix a problem with one of the orphaned checks failing if the intereaction_data tests are run in isolation. When setting a user as signed in, both their authentication level and their
* Add a test to make sure GET data is stripped from xhr_complete.
Make sure there is only one consecutive XHR event for a given URL.

fixes #3148
Merge pull request #3171 from mozilla/issue_3148_xhr_polling

Issue 3148 xhr polling

@kparlante gave the green light, I'm merging!

close #3148