[GD Cert] Support Python 3.9

* AOSP upgraded to Python 3.9 recently
* Use Python 3.9 as default test runner
* Modify logging lines in setup.py

Bug: 178410571
Tag: #gd-refactor
Test: gd/cert/run
Change-Id: I65cb619d747102d8f145511feb20a40d8bf38790