Fix race in DockerExternalGraphdriverSuite.TestExternalGraphDriver

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

integration-cli/docker_cli_external_graphdriver_unix_test.go

@@ -348,7 +348,7 @@ func (s *DockerExternalGraphdriverSuite) testExternalGraphDriver(name string, ex
 		c.Assert(err, check.IsNil, check.Commentf("\n%s", string(b)))
 	}
 
-	out, err := s.d.Cmd("run", "-d", "--name=graphtest", "busybox", "sh", "-c", "echo hello > /hello")
+	out, err := s.d.Cmd("run", "--name=graphtest", "busybox", "sh", "-c", "echo hello > /hello")
 	c.Assert(err, check.IsNil, check.Commentf(out))
 
 	err = s.d.Restart("-s", name)
@@ -359,7 +359,7 @@ func (s *DockerExternalGraphdriverSuite) testExternalGraphDriver(name string, ex
 
 	out, err = s.d.Cmd("diff", "graphtest")
 	c.Assert(err, check.IsNil, check.Commentf(out))
-	c.Assert(strings.Contains(out, "A /hello"), check.Equals, true)
+	c.Assert(strings.Contains(out, "A /hello"), check.Equals, true, check.Commentf("diff ouput: %s", out))
 
 	out, err = s.d.Cmd("rm", "-f", "graphtest")
 	c.Assert(err, check.IsNil, check.Commentf(out))