Refactor: Resolve Flake8 F401 and F403 and F405

Refactor: Resolve Flake8 F401 and F403 and F405

It's bad practice to use * imports (F405) since the methods or
variables being imported could be undefined. Explicitly importing
makes this more clear. Also F403 violation makes it difficult to
detect undefined names.

Additionally F401 violation to allow an indirect module import makes
things harder to debug. It's better to be explicit.

https://www.flake8rules.com/rules/F401.html
https://www.flake8rules.com/rules/F403.html
https://www.flake8rules.com/rules/F405.html

Change-Id: Ib938f865d3ac6456216a119c830d3b013932bf88
Signed-off-by: Thanh Ha <zxiiro@gmail.com>