Rename various variable so they do not shadow

Summary: As per title, this also uncovered a problem in the RPC code when dumping help for each method.

Test Plan:

make check

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: schancel, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1773