Update Upstart jobs

The previous Upstart jobs allowed privilege escalation via /tmp files abuse:

* the filename was predictable, so malicious processes would not have any trouble finding it.
* the file was sourced from a root /bin/sh, which means any process could replace the ip=${ip} bit with anything (most worrisome malicious commands).

It also has a few other cleanups, like making the instance variable name more obvious (PORT vs. p) and adding a `usage` stanza.