when topology.yaml is empty, 'tiup dm deploy' command should return a error or info to indicate this

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   [root@localhost ~]# tiup dm deploy localhost v3.0 aaa.yaml
   Starting component dm: /root/.tiup/components/dm/v1.1.2/tiup-dm deploy localhost v3.0 aaa.yaml
   Please confirm your topology:
   dm Cluster: localhost
   dm Version: v3.0
   Type Host Ports OS/Arch Directories

---

Attention:
1. If the topology is not what you expected, check your yaml file.
2. Please confirm there is no port/directory conflicts in same host.
Do you want to continue? [y/N]: y

• Generate SSH keys ... Done
• Download TiDB components
• Initialize target host environments
• Copy files
  Deployed cluster localhost successfully, you can start the cluster via tiup dm start localhost
  [root@localhost ~]# tiup dm start localhost
  Starting component dm: /root/.tiup/components/dm/v1.1.2/tiup-dm start localhost
  Starting cluster localhost...
• [ Serial ] - SSHKeySet: privateKey=/root/.tiup/storage/dm/clusters/localhost/ssh/id_rsa, publicKey=/root/.tiup/storage/dm/clusters/localhost/ssh/id_rsa.pub
• [ Serial ] - StartCluster
  Started cluster localhost successfully
  [root@localhost ~]#
  [root@localhost ~]# ls -ltr aaa.yaml
  -rw-r--r--. 1 root root 0 9月 14 10:20 aaa.yaml

2. What did you expect to see?

an info or error message returned

3. What did you see instead?

both deploy and start command execute successfully

4. What version of TiUP are you using (tiup --version)?
   [root@localhost ~]# tiup dm -v
   Starting component dm: /root/.tiup/components/dm/v1.1.2/tiup-dm -v
   tiup version v1.1.2 tiup
   Go Version: go1.13
   Git Branch: release-1.1
   GitHash: 7cb85b9-dirty
   [root@localhost ~]#