Use information stored in TestNode to connect nodes via p2p and RPC
Summary: As per title.
Test Plan:
./test/functional/test_runner.py --extended
Reviewers: #bitcoin_abc, jasonbcox, Fabien
Reviewed By: #bitcoin_abc, jasonbcox, Fabien
Subscribers: Fabien, jasonbcox, teamcity, schancel
Differential Revision: https://reviews.bitcoinabc.org/D2251