init: Add upstart init file

* Add an Upstart init file to reliably start and stop the container.

upstart.init

@@ -0,0 +1,8 @@
+# Copy to /etc/init/docker-openvpn.conf
+description "Docker container for OpenVPN server"
+start on filesystem and started docker
+stop on runlevel [!2345]
+respawn
+script
+  exec docker run --volumes-from ovpn-data --rm -p 1194:1194/udp --cap-add=NET_ADMIN kylemanna/openvpn
+end script