watchtower/blob/justice_kit: add BlobType to JusticeKit struct

This is preparation for later commits where the values returned by
member methods will need to be conditioned on the blob type used during
decryption.

watchtower/lookout/lookout_test.go

@@ -137,7 +137,9 @@ func TestLookoutBreachMatching(t *testing.T) {
 	}
 
 	// Construct a justice kit for each possible breach transaction.
+	blobType := blob.FlagCommitOutputs.Type()
 	blob1 := &blob.JusticeKit{
+		BlobType:         blobType,
 		SweepAddress:     makeAddrSlice(22),
 		RevocationPubKey: makePubKey(1),
 		LocalDelayPubKey: makePubKey(1),
@@ -145,6 +147,7 @@ func TestLookoutBreachMatching(t *testing.T) {
 		CommitToLocalSig: makeArray64(1),
 	}
 	blob2 := &blob.JusticeKit{
+		BlobType:         blobType,
 		SweepAddress:     makeAddrSlice(22),
 		RevocationPubKey: makePubKey(2),
 		LocalDelayPubKey: makePubKey(2),
@@ -156,13 +159,13 @@ func TestLookoutBreachMatching(t *testing.T) {
 	key2 := blob.NewBreachKeyFromHash(&hash2)
 
 	// Encrypt the first justice kit under breach key one.
-	encBlob1, err := blob1.Encrypt(key1, blob.FlagCommitOutputs.Type())
+	encBlob1, err := blob1.Encrypt(key1)
 	if err != nil {
 		t.Fatalf("unable to encrypt sweep detail 1: %v", err)
 	}
 
 	// Encrypt the second justice kit under breach key two.
-	encBlob2, err := blob2.Encrypt(key2, blob.FlagCommitOutputs.Type())
+	encBlob2, err := blob2.Encrypt(key2)
 	if err != nil {
 		t.Fatalf("unable to encrypt sweep detail 2: %v", err)
 	}