integration: fix flaky TestSwarmServiceWithGroup

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

integration-cli/docker_cli_swarm_test.go

@@ -225,7 +225,7 @@ func (s *DockerSwarmSuite) TestSwarmServiceWithGroup(c *check.C) {
 	d := s.AddDaemon(c, true, true)
 
 	name := "top"
-	out, err := d.Cmd("service", "create", "--name", name, "--user", "root:root", "--group-add", "wheel", "--group-add", "audio", "--group-add", "staff", "--group-add", "777", "busybox", "sh", "-c", "id > /id && top")
+	out, err := d.Cmd("service", "create", "--name", name, "--user", "root:root", "--group-add", "wheel", "--group-add", "audio", "--group-add", "staff", "--group-add", "777", "busybox", "top")
 	c.Assert(err, checker.IsNil)
 	c.Assert(strings.TrimSpace(out), checker.Not(checker.Equals), "")
 
@@ -238,7 +238,7 @@ func (s *DockerSwarmSuite) TestSwarmServiceWithGroup(c *check.C) {
 
 	container := strings.TrimSpace(out)
 
-	out, err = d.Cmd("exec", container, "cat", "/id")
+	out, err = d.Cmd("exec", container, "id")
 	c.Assert(err, checker.IsNil)
 	c.Assert(strings.TrimSpace(out), checker.Equals, "uid=0(root) gid=0(root) groups=10(wheel),29(audio),50(staff),777")
 }