Fix transaction logs incorrectly marked successful

[nick-mobilecoin]

Previously transaction_logs were marked successful if the input TXO(s)
were spent according to the block chain. This was problematic when
multiple transaction_logs were created that utilized the same input
TXOs. These transaction_logs using the same input TXOs could happen
when two clients were talking to the same Full-Service instance and
those clients were using two step build and submit:

1. Client_a sends build_transaction, input TXO_n is used
2. Client_b sends build_transaction, input TXO_n is also used
3. Client_a submit_transaction
4. Client_b submit_transaction before the block chain knows that the
   Client_a transaction exists and will consume TXO_n. The blockchain
   will still reject this transaction eventually.
5. Previously, Full-Service would see that input TXO_n has been consumed
   and will mark all submitted transaction_logs that used TXO_n as
   successful.

Now transaction_logs are marked successful based on if their output
TXO(s) land on the blockchain. This ensures that only the transaction
log that the blockchain accepted will be marked as successful.

[holtzman]

Looks good!

I think failing a tranasction_log where the input is spent and the output is not present in the same block would be good for the case where 2x full-service with the same account keys are running together, which is a situation that inspired this PR.

That said, this PR fixes a bug whereas that would be an improvement, allowing the full-service with the failed tx to recognize it sooner, so could be the subject of a future PR.