autopep8 test_framework.py

Summary: As per title.

Test Plan:

../qa/pull-tester/rpc-tests.py abc-p2p-fullblocktest.py

Reviewers: freetrader, #bitcoin_abc, CCulianu

Reviewed By: #bitcoin_abc, CCulianu

Subscribers: CCulianu

Differential Revision: https://reviews.bitcoinabc.org/D410