RFR: JDK-8230629: jpackage signing on macOS does not work as expected

[Alexander Matveev]

Please review the jpackage fix for bug [1] at [2].

This is a fix for the JDK-8200758-branch branch of the open sandbox 
repository (jpackage).

- Binaries in runtime and Frameworks will not be signed directly using 
user provided certificate.
- libapplauncher.dylib will be signed with user provided certificate 
only if it is unsigned.
- When signing is enabled app and pkg will be signed, but not dmg. App 
inside pkg and dmg will be signed as well.

[1] https://bugs.openjdk.java.net/browse/JDK-8230629

[2] http://cr.openjdk.java.net/~almatvee/8230629/webrev.00/

Thanks,
Alexander