[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:

• [x] I have read the contribution guidelines.
• [x] I have updated the documentation, if applicable.
• [x] I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• [x] 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[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: lucafascione / name: Luca Fascione (1fdbcfc627d3dba3545c0f50892daf70d550cf68, 5d5806bf89d151a9980f798b915b498b2f973e24)