Code review comment for lp:~allenap/launchpad/ddebs-n-udebs-go-shopping-bug-886452

Julian, I got a weird test failure in this branch which doesn't appear to be related to my change. Nevertheless, I've had a stab at fixing it, though I'm not sure that my solution is the best way to do so. Please could you look at the changes I made to test_twistedsftp.py?