Bug 873007 - Intermittent Jetpack tests/test-windows.testActiveWindow

* Adding more asserts to help us debug if intermittent fails continue
* Minor modification to order of window closing, to avoid unnecessary focus changing
* using setTimeout before nextStep since the latter is called during onFocus
* adding tests that the windows actually close before calling done
Merge pull request #1190 from erikvold/873007

Bug 873007 - Intermittent Jetpack tests/test-windows.testActiveWindow r=@Mossop