change tracker.py

[kitty-eu-org]

The tacker.py modified by the dmlc-core project fixes the tracker process exit problem caused by other programs accessing the port occupied by the tracker, and changes it to a more friendly prompt, allowing users to better troubleshoot. You can check the issue for details

[wbo4958]

@hezhaozhao-git Could you not change the format of python which makes the PR hard to review.

[kitty-eu-org]

@hezhaozhao-git你能不能不改变python的格式，这使得PR难以审查。

Ok, let me revise it

[ICDI0906]

great job！ I occur the same problem. but the format of pr is difficult to read what has changed. Can you change it?