[avalanche] Make the abc_p2p_avalanche_transaction_finalization.py test cases independant from each other

Summary: This makes the tests easier to reason about. The block full and min tx fee cases have huge impact on the node behavior due to the options they use, so it's better to restart between these cases. This makes the test run slower unfortunately, but it also makes it possible to split it into several files if needed.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_transaction_finalization

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18208