Chectest.py wasn't able to catch bug [1] as it didn't take into
consideration inheritance during the test discovery.
The cause of the issue is the fact that chectest.py parsed python files
by itself to discover the tests. This patch fixes this by using unittest
library for test discovery instead.
[1] https://review.opendev.org/c/osf/interop/+/806178
Story: 2009146
Task: 43097
Change-Id: I6e1b11eeb3ca1915ca41b6af88f9f568e6d674eb