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.