[backport#16551] test: Pass down correct chain name in tests
Summary:
https://github.com/bitcoin/bitcoin/pull/16551/commits/fa31dc1bf4ee471c4641eef8de02702ba0619ae7
Partial backport of Core PR16551
Test Plan:
./test/functional/test_runner.py
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D6430