Also add the uahfstarttime to the rpc test framework

Summary: This will boot node with a proper uahfstarttime by default. This put a lot of test back to green now that we passed the fork date.

Test Plan:

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

See that there are more green tests than before.

Reviewers: freetrader, #bitcoin_abc, CCulianu

Reviewed By: #bitcoin_abc, CCulianu

Subscribers: CCulianu, sickpig

Differential Revision: https://reviews.bitcoinabc.org/D411