lnd+lnwallet: extract default wallet password vars into lnwallet

lnd.go

@@ -196,8 +196,8 @@ func lndMain() error {
 	proxyOpts := []grpc.DialOption{grpc.WithTransportCredentials(cCreds)}
 
 	var (
-		privateWalletPw = []byte("hello")
-		publicWalletPw  = []byte("public")
+		privateWalletPw = lnwallet.DefaultPrivatePassphrase
+		publicWalletPw  = lnwallet.DefaultPublicPassphrase
 		birthday        time.Time
 		recoveryWindow  uint32
 	)

lnwallet/interface.go

@@ -11,10 +11,6 @@ import (
 	"github.com/roasbeef/btcutil"
 )
 
-// ErrNotMine is an error denoting that a WalletController instance is unable
-// to spend a specified output.
-var ErrNotMine = errors.New("the passed output doesn't belong to the wallet")
-
 // AddressType is an enum-like type which denotes the possible address types
 // WalletController supports.
 type AddressType uint8
@@ -32,10 +28,24 @@ const (
 	UnknownAddressType
 )
 
-// ErrDoubleSpend is returned from PublishTransaction in case the
-// tx being published is spending an output spent by a conflicting
-// transaction.
-var ErrDoubleSpend = errors.New("Transaction rejected: output already spent")
+var (
+	// DefaultPublicPassphrase is the default public passphrase used for the
+	// wallet.
+	DefaultPublicPassphrase = []byte("public")
+
+	// DefaultPrivatePassphrase is the default private passphrase used for
+	// the wallet.
+	DefaultPrivatePassphrase = []byte("hello")
+
+	// ErrDoubleSpend is returned from PublishTransaction in case the
+	// tx being published is spending an output spent by a conflicting
+	// transaction.
+	ErrDoubleSpend = errors.New("Transaction rejected: output already spent")
+
+	// ErrNotMine is an error denoting that a WalletController instance is
+	// unable to spend a specified output.
+	ErrNotMine = errors.New("the passed output doesn't belong to the wallet")
+)
 
 // Utxo is an unspent output denoted by its outpoint, and output value of the
 // original output.