chainntnfs: update confirm ntfn tests to verify TxIndex+BlockHeight
chainntnfs: update confirm ntfn tests to verify TxIndex+BlockHeight

This commit updates two interface-level tests for confirmation
notifications to check the txIndex and blockHeight advertised to serve
as regression tests for the recent bug fix related to properly setting
these two fields.

ddustin/lnd,AndrewSamokhvalov/lnd,aakselrod/lnd,aakselrod/lnd,LightningNetwork/lnd,ddustin/lnd,AndrewSamokhvalov/lnd,LightningNetwork/lnd