[wallet] [test] Add listwallets RPC, include wallet name in getwalletinfo and add multiwallet test.

Summary: This backports core's PR10604 and fixes T172.

Test Plan:

make check
./test/functional/test_runner.py multiwallet

Reviewers: #bitcoin_abc, matiu, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, matiu, teamcity

Maniphest Tasks: T172

Differential Revision: https://reviews.bitcoinabc.org/D1035