Refactored existing monolith_opcodes tests

Summary:
These changes are needed in order to merge D1212 and D1097

Co-authored-by: Joshua Yabut <yabut.joshua@gmail.com>
Co-authored-by: Marcos Mayorga <mm@mm-studios.com>

Test Plan: make check

Reviewers: deadalnix, schancel, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1223