lnwallet: return our final local balance from CompleteCooperativeClose

In this commit, add an additional return value to
CompleteCooperativeClose. We’ll now report to the caller our final
balance in the cooperative closure transaction. We report this as
depending on if we’re the initiator or not, our final balance may not
exactly match the balance we had in the last state.

lnwallet/channel_test.go

@@ -904,7 +904,7 @@ func TestCooperativeChannelClosure(t *testing.T) {
 	// With the proposals created, both sides should be able to properly
 	// process the other party's signature. This indicates that the
 	// transaction is well formed, and the signatures verify.
-	aliceCloseTx, err := bobChannel.CompleteCooperativeClose(
+	aliceCloseTx, _, err := bobChannel.CompleteCooperativeClose(
 		bobCloseSig, aliceCloseSig, bobDeliveryScript,
 		aliceDeliveryScript, bobFee)
 	if err != nil {
@@ -912,7 +912,7 @@ func TestCooperativeChannelClosure(t *testing.T) {
 	}
 	bobCloseSha := aliceCloseTx.TxHash()
 
-	bobCloseTx, err := aliceChannel.CompleteCooperativeClose(
+	bobCloseTx, _, err := aliceChannel.CompleteCooperativeClose(
 		aliceCloseSig, bobCloseSig, aliceDeliveryScript,
 		bobDeliveryScript, aliceFee)
 	if err != nil {
@@ -2019,7 +2019,7 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	}
 	bobCloseSig := append(bobSig, byte(txscript.SigHashAll))
 
-	closeTx, err := bobChannel.CompleteCooperativeClose(
+	closeTx, _, err := bobChannel.CompleteCooperativeClose(
 		bobCloseSig, aliceCloseSig,
 		bobDeliveryScript, aliceDeliveryScript, bobFee)
 	if err != nil {
@@ -2057,7 +2057,7 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	}
 	bobCloseSig = append(bobSig, byte(txscript.SigHashAll))
 
-	closeTx, err = bobChannel.CompleteCooperativeClose(
+	closeTx, _, err = bobChannel.CompleteCooperativeClose(
 		bobCloseSig, aliceCloseSig,
 		bobDeliveryScript, aliceDeliveryScript, bobFee)
 	if err != nil {
@@ -2099,7 +2099,7 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	}
 	bobCloseSig = append(bobSig, byte(txscript.SigHashAll))
 
-	closeTx, err = bobChannel.CompleteCooperativeClose(
+	closeTx, _, err = bobChannel.CompleteCooperativeClose(
 		bobCloseSig, aliceCloseSig,
 		bobDeliveryScript, aliceDeliveryScript, bobFee)
 	if err != nil {