itest: RegisterSpendNtfn detects reorgs

Added itest "reorg_notifications" which tests that RegisterSpendNtfn behaves as
expected during a reorg. A reorg notification is produced after a reorg affects
the block which has produced a spending notification for this registration.

itest/list_on_test.go

@@ -46,6 +46,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "send selected coins channel reserve",
 		TestFunc: testSendSelectedCoinsChannelReserve,
 	},
+	{
+		Name:     "reorg notifications",
+		TestFunc: testReorgNotifications,
+	},
 	{
 		Name:     "disconnecting target peer",
 		TestFunc: testDisconnectingTargetPeer,