Replay Stage start_leader() can use wrong parent fork() (#3238)

*  Make sure start_leader starts on the last voted block, not necessarily the biggest indexed bank in frozen_slots()

* Fix tvu test

core/src/poh_service.rs

@@ -110,7 +110,8 @@ mod tests {
         let (genesis_block, _mint_keypair) = GenesisBlock::new(2);
         let bank = Arc::new(Bank::new(&genesis_block));
         let prev_hash = bank.last_blockhash();
-        let (poh_recorder, entry_receiver) = PohRecorder::new(bank.tick_height(), prev_hash);
+        let (poh_recorder, entry_receiver) =
+            PohRecorder::new(bank.tick_height(), prev_hash, bank.slot());
         let poh_recorder = Arc::new(Mutex::new(poh_recorder));
         let exit = Arc::new(AtomicBool::new(false));
         let working_bank = WorkingBank {