Bug 1100390: Create a new test case for the deletion of video from Preview

Squashed commit from original 1100390 pull request
Please update this wait to the new syntax, as in https://github.com/npark-mozilla/gaia/blob/1100390_2ndAttempt/tests/python/gaia-ui-tests/gaiatest/tests/functional/camera/test_camera_delete_captured_video.py#L56