Temporarily disable reading of consensus.h from Python test framework

Summary:
Temporarily disable reading of consensus.h from Python test framework
This breaks if tests are not executed from top-level.

Test Plan: qa/pull-tester/rpc-tests.py -extensive

Reviewers: #bitcoin_abc, deadalnix, sickpig, kyuupichan

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D168