AndroidRunner: Fix CheckPidTimer to not fire forever

- Only start the timer after we are sure that the app is running.
- Stop the timer if we detect that the app was closed.

Task-number: QTCREATORBUG-9545
Change-Id: I7d08b759d3aa5baaa3f82ee09aefb17e7c5fb512
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>