I have no idea who creates the /run/openvpn directory on Debian.
The path is not in a tmpfiles.d and I don't see the generator
creating it or the service file indicating that it needs to be
created. Place the file with openvpn.NAME.status into the /run
directory which appears to work on the device.
We want to use systemd for managing the lifetime of OpenVPN. Take
the debian generator (which should work with busybox ash) and the
openvpn.service (to inhibit the sysvinit script) and the target
file and install it.
On systems that have ran "update-rc.d openvpn defaults" one need
to manually execute a systemctl enable openvpn.service. This is
not done through a post-inst script and I am not sure if we should
do it. This means there is a danger of ending with a unit that
doesn't start OpenVPN automatically after upgrade!
The scripts/packages have not been tested on a device yet.