Improve verbose logging for transactions when rollback is required

While working on a MongoDB test failure, I tried to use transaction-level verbose logging but found out that the current coverage is not quite up to the mark. Most of the existing logging is written around prepared transactions and there is very limited functionality for other use cases. 

The aim of this ticket is to review the transaction module and insert verbose logging messages where appropriate. As a starter, a patch is attached to the ticket that was used to debug the MongoDB test failure mentioned above.