utxonursery: configure using SweepInput function

As a preparation for mocking sweeper, this commit modifies the
utxonursery config to take a function pointer instead of the full
sweeper struct.

server.go

@@ -636,7 +636,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB, cc *chainControl,
 		Notifier:            cc.chainNotifier,
 		PublishTransaction:  cc.wallet.PublishTransaction,
 		Store:               utxnStore,
-		Sweeper:             s.sweeper,
+		SweepInput:          s.sweeper.SweepInput,
 	})
 
 	// Construct a closure that wraps the htlcswitch's CloseLink method.

utxonursery.go

@@ -195,9 +195,8 @@ type NurseryConfig struct {
 	// maintained about the utxo nursery's incubating outputs.
 	Store NurseryStore
 
-	// Sweeper provides functionality to generate sweep transactions.
-	// Nursery uses this to sweep final outputs back into the wallet.
-	Sweeper *sweep.UtxoSweeper
+	// Sweep sweeps an input back to the wallet.
+	SweepInput func(input sweep.Input) (chan sweep.Result, error)
 }
 
 // utxoNursery is a system dedicated to incubating time-locked outputs created
@@ -803,7 +802,7 @@ func (u *utxoNursery) sweepMatureOutputs(classHeight uint32,
 		// passed in with disastruous consequences.
 		local := output
 
-		resultChan, err := u.cfg.Sweeper.SweepInput(&local)
+		resultChan, err := u.cfg.SweepInput(&local)
 		if err != nil {
 			return err
 		}

utxonursery_test.go

@@ -488,9 +488,9 @@ func createNurseryTestContext(t *testing.T,
 				CloseHeight: 0,
 			}, nil
 		},
-		Store:   storeIntercepter,
-		ChainIO: chainIO,
-		Sweeper: sweeper,
+		Store:      storeIntercepter,
+		ChainIO:    chainIO,
+		SweepInput: sweeper.SweepInput,
 		PublishTransaction: func(tx *wire.MsgTx) error {
 			return publishFunc(tx, "nursery")
 		},
@@ -556,7 +556,7 @@ func createNurseryTestContext(t *testing.T,
 			}
 
 			/// Restart nursery.
-			nurseryCfg.Sweeper = ctx.sweeper
+			nurseryCfg.SweepInput = ctx.sweeper.SweepInput
 			ctx.nursery = newUtxoNursery(&nurseryCfg)
 			ctx.nursery.Start()