8237607: [macos] Signing app bundle with jpackage fails if runtime is already signed

Reviewed-by: herrick, asemenyuk, kcr

Author: Alexander Matveev

src/jdk.incubator.jpackage/macosx/classes/jdk/incubator/jpackage/internal/MacAppImageBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -823,6 +823,7 @@ public static void signAppBundle(
             try {
                 List<String> args = new ArrayList<>();
                 args.addAll(Arrays.asList("codesign",
+                        "-f",
                         "-s", signingIdentity, // sign with this key
                         "--prefix", identifierPrefix,
                         // use the identifier as a prefix