lnd: modify htlc error integration tests to account for max payment size
lnd: modify htlc error integration tests to account for max payment size

This commit modifies the HTLC integration tests to be mindful of the
max payment size. Rather than sending the payment in one large batch,
we instead now send it in chunks of the max payment size.

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