There are two different ways we used to stop a application:
am force-stop $packageName or kill -9 applicationPid. As far as I
remember that's because on some devices some one of them didn't work.
The code wasn't consistently using both though. Fix that by making it
one function, which uses both and use that one consistently.

Task-number: QTCREATORBUG-10557
Change-Id: Ib09a51e2bddae8d28a5d234e792906cc03606fda
Reviewed-by: BogDan Vatra <bogdan@kde.org>