Synchronized upstart script with the one recommended by nginx.

This fixes problems with nginx respawning too many times because upstart was not tracking the process correctly.

http://wiki.nginx.org/Upstart

You can test this by ensuring that the process id of the nginx master matches what is being reported by upstart (i.e. `service nginx status`). Also verify that nginx is not respawning repeatedly by looking in the `error.log` configured for nginx.