Prepare test scenarios for HF26 transaction serialization changes
We need to test old / new serialization scenarios including but not limited to:
- test old/new during hf25 rules (ie. before hardfork time)
- test old/new during hf25 rules, after the hardfork time, but before actual hardfork (that happens after scheduled time already passed but there's no supermajority of witnesses voting for hf26 yet)
- test old/new during hf26 rules, i.e. after hardfork actually happened