chaintnfs/interface_test: test notifiers handling missed blocks
chaintnfs/interface_test: test notifiers handling missed blocks

Tests for the case where a chain backend skips a series of blocks, such that the notifier's best block is out of date. Also tests the case where a notifier's best block has been reorged out of the chain.

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