* Added the end_run_all option for 2.4 release.

* Fixed a add_argument typo.

* Changed to use add_argument() compatible with python 3.8.

* reformat.

* Added docstring to explain the _end_run_clients().

* Added more explanation.

* reformat.

* rewrite the _end_run_clients() to make it easier to understand.

* reformat.

* adjust the locking in the _end_run_clients().

* fixed a potential None pointer error.

* renamed clients_finished_end_run variable.