Impact of the bug
WMAgent

Describe the bug
While working on the deployment documentation: #12161, I found some minor misconfiguration here when it comes to the virtual env. setup, like missing python paths for unit tests and/or not updated path for searching the WMAgent.secrerts file etc. I intend to pile them all in a single PR and resolve the current issue as a followup from the documentation one.

How to reproduce it
Not much to reproduce - some minor fixes at deployment time.

Expected behavior
To make the deployment right.

Additional context and error message
This is a follow up from: #12161