Stop using daemon mode in upstart scripts.

In daemon mode then upstart never detects if the container craps out / exits,
and therefore never respawns correctly (at least in the upstart version
in precise)..

I'd at least like to run containers not as a daemon - let me know if you
feel strongly about this, as I'm happy to supply an alternate patch allowing
both behaviours if there are cases where daemon mode is a good thing that
I'm not seeing ;)