Merge #11773: [tests] Change feature_block.py to use BitcoinTestFramework

Summary:
PR11773 backport https://github.com/bitcoin/bitcoin/pull/11773/files
265d7c4 [tests] Improve assert message when wait_until() fails (John Newbery)
ebf053a [tests] Change feature_block.py to use BitcoinTestFramework (John Newbery)
fc02c12 [tests] Add logging to feature_block.py (John Newbery)
3898c4f [tests] Tidy up feature_block.py (John Newbery)
5cd01d2 [tests] Fix flake8 warnings in feature_block.py (John Newbery)

Pull request description:

Next step in #10603.

- first three commits tidy up feature_block.py
- fourth commit removes usage of ComparisonTestFramework

Longer term, it would be better to separate net_processing testing from validation testing, but I think this is still a useful PR, since it moves us away from the comparison test framework.

Test Plan: test_runner.py feature_block.py

Reviewers: deadalnix, Fabien, jasonbcox, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Maniphest Tasks: T669

Differential Revision: https://reviews.bitcoinabc.org/D3514