Make upstart track the wikimetrics PID

The “script” clause caused upstart to spawn a shell, which then
spawned wikimetrics. Upstart tracked only the wrapping shell. Upon
stopping the queue, the shell got killed, but the wikimetrics queue
process survived, and upstart did not care. Such hanging queue
processes confused wikimetrics. We now skip the unneeded wrapping
shell and have upstart correctly track the wikimetrics process
directly. Thereby, stopping the queue works reliably.

Bug: 63819
Change-Id: I6bf30b9562eeec2b513edc8b70938c63b1564c76