Update Python Client SDK for Tester

## Motivation &nbsp;

- To develop [Backend.AI](http://Backend.AI) Tester based on the Python Client SDK, it is first necessary to validate the Python Client SDK.
- There may be some missing code in the current Python SDK, and some methods might be outdated and not functioning properly.

## Objective &nbsp;

- Let's update the outdated code and fill in the missing parts.
