chainntnfs/bitcoind: move NotifySpent to after recording the outpoint
chainntnfs/bitcoind: move NotifySpent to after recording the outpoint

This commit moves the call to the bitcoind backend to start watching an
outpoint for spentness to after we have recorded the outpoint in our
list of clients. This is done to avoid a race that we saw using the btcd
backend, and it is probable that it can also happen using bitcoind.

aakselrod/lnd,aakselrod/lnd,LightningNetwork/lnd,LightningNetwork/lnd