multi: add preimage push to loop out after sweep attempt

Once we have revealed our preimage to the world with a sweep attempt,
we can safely push our preimage to the server to speed up on chain
claim.

Rather than rely on the server, we use the state of our invoice in lnd
to determine whether we should continue trying to push the preimage to
the server.

client_test.go

@@ -12,7 +12,9 @@ import (
 	"github.com/lightninglabs/loop/lndclient"
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/test"
+	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/stretchr/testify/require"
 )
 
 var (
@@ -261,6 +263,10 @@ func testSuccess(ctx *testContext, amt btcutil.Amount, hash lntypes.Hash,
 
 	ctx.AssertRegisterSpendNtfn(confIntent.PkScript)
 
+	// Assert that a call to track payment was sent, and respond with status
+	// in flight so that our swap will push its preimage to the server.
+	ctx.trackPayment(lnrpc.Payment_IN_FLIGHT)
+
 	// Publish tick.
 	ctx.expiryChan <- testTime
 
@@ -287,6 +293,13 @@ func testSuccess(ctx *testContext, amt btcutil.Amount, hash lntypes.Hash,
 		ctx.T.Fatalf("incorrect preimage")
 	}
 
+	// Since we successfully published our sweep, we expect the preimage to
+	// have been pushed to our mock server.
+	preimage, err := lntypes.MakePreimage(clientPreImage)
+	require.NoError(ctx.T, err)
+
+	ctx.assertPreimagePush(preimage)
+
 	// Simulate server pulling payment.
 	signalSwapPaymentResult(nil)