Ensure /var/run/app_name/ exists when starting

On Debian, /var/run is a symbolic link to /run which is [actually a tmpfs](https://wiki.debian.org/ReleaseGoals/RunDirectory#Overview). So after system reboot, the /var/run/app_name directory doesn't exist anymore, leading to the following error:

	start-stop-daemon: unable to open pidfile '/var/run/app_name/running.pid' for writing (No such file or directory)