SSH into test vms on gce as 'vagrant' user

test/gce.sh

@@ -140,7 +140,7 @@ function hosts {
 		hosts="$hostname $hosts"
 		args="--add-host=$hostname:$(internal_ip $json $name) $args"
 	done
-	echo export SSH=ssh
+	echo export SSH=\"ssh -l vagrant\"
 	echo export HOSTS=\"$hosts\"
 	echo export ADD_HOST_ARGS=\"$args\"
 	rm $json