run-tests: auto-replace 'TXNID' output
Hooks related to the transaction are aware of the transaction id. By definition
this txn-id is unique and different for each transaction. As a result it can
never be predicted in test and always needs matching. As a result, touching any
like with this data is annoying. We solve the problem once and for all by
installing an automatic replacement. In test, this will now show as:
TXNID=TXN:$ID$