Add exclude option to rpc-tests.py

Summary:
Backport the following commit from Bitcoin Core:

commit c5784085e9031ea1ad32a2aee897bd57a0482d24
Author: John Newbery <john@johnnewbery.com>
Date:   Wed Feb 15 09:59:19 2017 -0500

    Add exclude option to rpc-tests.py

Depends on D827.
Relates to T124.

Test Plan: Run RPC tests with an excluded test

Reviewers: deadalnix, Yura, akb, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D828