Add new test cases to abc-finalize-.py

Summary:
Add new test cases and assertions.
Also replace the sync_blocks calls with a proper wait_for_tip() function.

Depends on D2161

Test Plan:

./test/functional/test_runner.py abc-finalize-block

Reviewers: deadalnix, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2162