lnd test: add offline scenario to testDataLossProtection
lnd test: add offline scenario to testDataLossProtection

This adds the scenario where a channel is closed while the node is
offline, the node loses state and comes back online. In this case the
node should attempt to resync the channel, and the peer should resend a
channel sync message for the closed channel, such that the node can
retrieve its funds.

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