Add test coverage for messages requesting invalid blocks

Summary:
While digging around the net code and tests, I realized these cases are not covered.
There are related tests that cover similar code paths in p2p_fingerprint and others, but they
do not test this behavior explicitly.

Test Plan: test_runner.py abc-get-invalid-block

Reviewers: #bitcoin_abc, deadalnix, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4503