Rename test/pull-tester/rpc-tests.py to test/functional/test_runner.py

Summary:
Port the following commit from Bitcoin Core.

commit a9bd622a658b41b219912288e643f5e2c1b145b4
Author: John Newbery <john@johnnewbery.com>
Date:   Thu Mar 9 09:53:26 2017 -0500

    Rename test/pull-tester/rpc-tests.py to test/functional/test_runner.py

Depends on D831
Relates to T124

Test Plan: test/function/test_runner.py

Reviewers: deadalnix, Yura, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D832