[test] Add test for listaddressgroupings

Summary:
Test added as part of wallet-accounts.py.
Make file a little more flake8 compliant

Backport core's PR10255

Test Plan:

./test/functional/test_runner.py wallet-accounts

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1167