tiup-playground can't start tiflash with `--tag` specified

[lucklove]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

tiup --tag testv5 playground v5.0.0-20210403

ctrl + c

tiup --tag testv5 playground v5.0.0-20210403

2. What did you expect to see?

TiFlash should start success in both case.

3. What did you see instead?

TiFlash only start success in the first case:

4. What version of TiUP are you using (tiup --version)?

v1.4.0