[chronik] Remove some boilerplate from the test_framework

Summary: This refactor makes the tests slightly nicer to write and read, and will allow for leveraging the timeout factor for the chronik tests in a follow up.

Test Plan:

./test/functional/test_runner.py chronik_*

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14776