Bug 1028941 - gaiatest - Kill only FTU when doing restart, kill all runn...

...ing apps when doing a full reset
Would it be safer to add a new method for `kill_all_including_system`, as opposed to allowing `kill_all` to accept an argument? That would allow `kill_all` to maintain its current functionality (or at least the way we intended for it to currently work), and if someone really wants to kill everything then they could call `kill_all_including_system`. This would eliminate the chance that someone accidentally calls `kill_all` passing `True` by mistake.