TestContainerAPITop: fix flakyness

The following failure is seen in CI from time to time:

> FAIL: docker_api_containers_test.go:435: DockerSuite.TestContainerAPITop
>
> docker_api_containers_test.go:453:
>     c.Assert(top.Processes[0][10], checker.Equals, "/bin/sh -c top")
> ... obtained string = "top"
> ... expected string = "/bin/sh -c top"

The test case expects two processes in the output:

1. /bin/sh -c top
2. top

in the given order.

Now, "ps aux" output is sorted by PID*, and so since the "top" is a child
of "/bin/sh -c top" it has a higher PID and will come second as expected
by the test... unless the PIDs on the system are exhausted and PID rollover
happens, in which case PID of "top" will be lower than that of "/bin/sh".

Fix: sort output by process name.

* - in fact it is not sorted, but is being printed in the same order as
    the kernel list PID entries in /proc directory, which appears to be
    sorted by PID (see ls -1 -U /proc).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

integration-cli/docker_api_containers_test.go

@@ -442,7 +442,8 @@ func (s *DockerSuite) TestContainerAPITop(c *check.C) {
 	c.Assert(err, checker.IsNil)
 	defer cli.Close()
 
-	top, err := cli.ContainerTop(context.Background(), id, []string{"aux"})
+	// sort by comm[andline] to make sure order stays the same in case of PID rollover
+	top, err := cli.ContainerTop(context.Background(), id, []string{"aux", "--sort=comm"})
 	c.Assert(err, checker.IsNil)
 	c.Assert(top.Titles, checker.HasLen, 11, check.Commentf("expected 11 titles, found %d: %v", len(top.Titles), top.Titles))