Bug 1110102 - [v2.2] Add test to verify that the video recording stops i...

...mmediately when going to homescreen
As discussed on IRC, we already use this format in [https://github.com/mozilla-b2g/gaia/blob/master/tests/python/gaia-ui-tests/gaiatest/apps/videoplayer/regions/fullscreen_video.py#L26](FullscreenVideo). So it's better to stick to it.