utxonursery: use a two value read from the epoch chan for graceful shutdown
utxonursery: use a two value read from the epoch chan for graceful shutdown

Within the utoxNursery we now use a two value read fro the block epoch
channel in order to exit early if/when the ChainNotifier begins the
shutdown process before the signal reaches the utxoNursery.

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