Ensure all RPC tests consistently run with fork activation in the past.

Summary: This ensure they all test for the post fork logic rather than the prefork one.

Test Plan:

../qa/pull-tester/rpc-tests.py

Reviewers: freetrader, CCulianu, hanchon, #bitcoin_abc

Reviewed By: CCulianu, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D432