when tiup dm command is executed successfully, command help info should not displayed in response

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

execute 'tiup dm --wait-timeout 3'

2. What did you expect to see?

command success

3. What did you see instead?
   when command executed successfully, maybe help info should not be displayed in response.

[root@localhost ~]# tiup dm --wait-timeout 3
Starting component dm: /root/.tiup/components/dm/v1.1.2/tiup-dm --wait-timeout 3
Deploy a DM cluster (experimental)

Usage:
tiup dm [command]

Available Commands:
deploy Deploy a DM cluster for production
start Start a DM cluster
stop Stop a DM cluster
restart Restart a DM cluster
list List all clusters
destroy Destroy a specified DM cluster
audit Show audit log of cluster operation
exec Run shell command on host in the dm cluster
edit-config Edit DM cluster config
display Display information of a DM cluster
reload Reload a DM cluster's config and restart if needed
upgrade Upgrade a specified DM cluster
patch Replace the remote package with a specified package and restart the service
scale-out Scale out a DM cluster
scale-in Scale in a DM cluster
import Import an exist DM 1.0 cluster from dm-ansible and re-deploy 2.0 version
help Help about any command

Flags:
-h, --help help for tiup
--native-ssh Use the native SSH client installed on local system instead of the build-in one.
--ssh-timeout int Timeout in seconds to connect host via SSH, ignored for operations that don't need an SSH connection. (default 5)
-v, --version version for tiup
--wait-timeout int Timeout in seconds to wait for an operation to complete, ignored for operations that don't fit. (default 60)
-y, --yes Skip all confirmations and assumes 'yes'

Use "tiup dm help [command]" for more information about a command.
[root@localhost ~]#

4. What version of TiUP are you using (tiup --version)?
   [root@localhost ~]# tiup -v
   v1.0.9 tiup
   Go Version: go1.13
   Git Branch: master
   GitHash: 41fbacf
   [root@localhost ~]#

Start by reproducing tiup dm --wait-timeout 3 and trace the tiup dm command's success path to identify why help output is shown. Done means a successful command exits without printing the command help information.