fix test ps --before

Signed-off-by: Victor Vieux <vieux@docker.com>

test/integration/api/ps.bats

@@ -50,6 +50,7 @@ function teardown() {
 	swarm_manage
 
 	docker_swarm run -d --name c1 busybox echo c1
+	sleep 1 #sleep so the 2 containers don't start at the same second
 	docker_swarm run -d --name c2 busybox echo c2
 
 	run eval "docker_swarm ps --before c1 2>/dev/null"