Fix a bug I introduced with last commit which resulted in openvpn not
being started during boot. The reason for this is that at boot $0 is not
/usr/local/etc/rc.d/openvpn but /etc/rc. The fix is a bit hackish because
it retrieves the script name from $_file - variable used in run_rc_script().
Reported by: bazzoola <firstname.lastname@example.org>