Ensure that new mocknet test is passing for 1.40.0-testing branch

[posvyatokum]

As we transition to the new way of doing a mirror test via fast forknet setup, I want to run the new test version for 1.40.0 release as well.
The goal of this issue is to discover incompatibilities between the new setup and release testing, and create comprehensive instructions on running the new mirror test for future release engineers.
The byproduct of this issue would be more confidence in the release.