exp/ssh: change test listen address, also exit test if fails
exp/ssh: change test listen address, also exit test if fails

R=golang-dev, rsc
CC=dave, golang-dev
http://codereview.appspot.com/5364061
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go