A pack of nits

Summary: Various small changes such as formatting, modernizing loops, etc...

Test Plan:

make check
../qa/pull-tester/rpc-tests.py

Reviewers: freetrader, dagurval, schancel, #bitcoin_abc, zquestz

Reviewed By: dagurval, #bitcoin_abc, zquestz

Subscribers: zquestz

Differential Revision: https://reviews.bitcoinabc.org/D557