[tests] Add p2p connection to TestNode
Summary:
Partial backport of core PR11182
(commits 5e5725c and b86c1cd)
p2p connections can now be added to TestNode instances. This commit also updates the example test to use the new p2p interface in TestNode to demonstrate usage. A future commit will update the existing tests to use p2p through the TestNode.
Test Plan:
./test/functional/test_runner.py example_test
Reviewers: #bitcoin_abc, deadalnix, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Subscribers: jasonbcox, teamcity, schancel
Differential Revision: https://reviews.bitcoinabc.org/D2326