[CI] Run functional tests bost pre and post great wall

Summary:
This will run the functional tests twice, once without great wall
activation (up the flag day), and once with great wall activated.
Issues occurring from the great wall update can be catched before the
flag day, while keeping the current regression testing effective.

Depends on D2518

Test Plan: Read the teamcity build log

Reviewers: jasonbcox, deadalnix, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2460