Fix and support python2.x or python3.9 on yarn.

[rryqszq4]

Fix no module named 'main.util' that not found file util on yarn.

Fix should be classpath and not class_path.

Support python2.x and python3.9 such as change threading.isAlive to is_alive(https://github.com/python/cpython/blob/87109f4d85c93a870ee8aa0d2b394547d4636b17/Doc/whatsnew/3.9.rst#id717), or change subprocess.call to subprocess.Popen because no args 'env' at method call in python2.x .

[rryqszq4]

I wonder why there's still a need to support py2 since it has reached end of life.

@szha Because our cluster env was python2, i try to run on yarn but failed, so i fix some problem. Just found this issues #565 but i know it's important for me, so i need fix it.

[hcho3]

Closing, as the pull request has been stable. Feel free to re-submit if the change is still necessary. Thanks!