The young person's guide to the test_framework

Summary: Backport core's PR10612 and PR11025

Test Plan:

make check
./test/functional/test_runner.py

Reviewers: #bitcoin_abc, schancel, jasonbcox

Reviewed By: #bitcoin_abc, schancel, jasonbcox

Subscribers: jasonbcox, schancel, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1063