utxonursery: update output sweeping to be aware of new output types

In this commit, we modify the logic surrounding sweeping outputs to be
aware of the new types of outputs that the nursery is now responsible
for. Namely: incoming HTLC’s on our commitment transaction as well as
outgoing HTLC’s on the commitment transaction for the remote party. For
 the latter class of HTLC, we’ll now set the lock time on the sweeping
transaction in order to satisfy the CLTV clause in the output we’re
spending.