on boot, ensure processes managed by upstart run after all network interfaces are up

* the existing config only waited until the loopback interface was
  ready, causing some processes to fail to start
* the static-network-up event has been available since upstart 1.3 in
  Ubuntu 11.10. It is emitted when all statically configured interfaces
  are up and ready
* This wouldn't be appropriate for all upstart processes, but we're a web
  company and all our stuff requires the network