lnd_test: correct that Bob can sweep immediately
lnd_test: correct that Bob can sweep immediately

This commit fixes a flake within the integration tests, where we would
mine a set of blocks before checking if Bob's sweep tx was in the
mempool. Usually this would pass since the blocks were generated before
the tx hit the miner's mempool, but sometimes it was mined and then we
would check the mempool.

This commit fixes this by correctly waiting immediately for Bob to sweep
his funds, as they are not time locked.

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