[test] Added a few improvements to runtest.py test runner

[lucafascione]

Description

I made a few changes to runtest.py that should improve its usefulness.
However I also changed its output a bit, and I would like to change it some more.
The branch is meant to verify that these changes don't disturb the rest of CI system

Checklist:

• I have read the contribution guidelines.
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• My code follows the prevailing code style of this project. If I haven't
  already run clang-format v17 before submitting, I definitely will look at
  the CI test that runs clang-format and fix anything that it highlights as
  being nonconforming.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: lucafascione / name: Luca Fascione (85cac21)