sweep: delay sweeping inputs with future locktimes

This commit fixes an edge case that the sweeper's best known block
height is behind arbitrator's, which may cause an issue when creating
sweeping tx, as we may end up using an old block height from
arbitrator's view.

sweep/sweeper_test.go

@@ -2478,14 +2478,40 @@ func TestUpdateSweeperInputs(t *testing.T) {
 	// Create a test sweeper.
 	s := New(nil)
 
+	// Create mock inputs.
+	inp1 := &input.MockInput{}
+	defer inp1.AssertExpectations(t)
+	inp2 := &input.MockInput{}
+	defer inp2.AssertExpectations(t)
+
 	// Create a list of inputs using all the states.
-	input0 := &SweeperInput{state: Init}
-	input1 := &SweeperInput{state: PendingPublish}
-	input2 := &SweeperInput{state: Published}
-	input3 := &SweeperInput{state: PublishFailed}
-	input4 := &SweeperInput{state: Swept}
-	input5 := &SweeperInput{state: Excluded}
-	input6 := &SweeperInput{state: Failed}
+	//
+	// Mock the input to have a locktime that's matured so it will be
+	// returned.
+	inp1.On("RequiredLockTime").Return(
+		uint32(s.currentHeight), false).Once()
+	input0 := &SweeperInput{state: Init, Input: inp1}
+
+	// These inputs won't hit RequiredLockTime so we won't mock.
+	input1 := &SweeperInput{state: PendingPublish, Input: inp1}
+	input2 := &SweeperInput{state: Published, Input: inp1}
+
+	// Mock the input to have a locktime that's matured so it will be
+	// returned.
+	inp1.On("RequiredLockTime").Return(
+		uint32(s.currentHeight), false).Once()
+	input3 := &SweeperInput{state: PublishFailed, Input: inp1}
+
+	// These inputs won't hit RequiredLockTime so we won't mock.
+	input4 := &SweeperInput{state: Swept, Input: inp1}
+	input5 := &SweeperInput{state: Excluded, Input: inp1}
+	input6 := &SweeperInput{state: Failed, Input: inp1}
+
+	// Mock the input to have a locktime in the future so it will NOT be
+	// returned.
+	inp2.On("RequiredLockTime").Return(
+		uint32(s.currentHeight+1), true).Once()
+	input7 := &SweeperInput{state: Init, Input: inp2}
 
 	// Add the inputs to the sweeper. After the update, we should see the
 	// terminated inputs being removed.
@@ -2497,6 +2523,7 @@ func TestUpdateSweeperInputs(t *testing.T) {
 		{Index: 4}: input4,
 		{Index: 5}: input5,
 		{Index: 6}: input6,
+		{Index: 7}: input7,
 	}
 
 	// We expect the inputs with `Swept`, `Excluded`, and `Failed` to be
@@ -2506,6 +2533,7 @@ func TestUpdateSweeperInputs(t *testing.T) {
 		{Index: 1}: input1,
 		{Index: 2}: input2,
 		{Index: 3}: input3,
+		{Index: 7}: input7,
 	}
 
 	// We expect only the inputs with `Init` and `PublishFailed` to be