RFR: JDK-8244576: [macos] Volume icon deleted by osascript for background image

[Andy Herrick]

Please review jpackage fix for issue [1] at [2].

[1] - https://bugs.openjdk.java.net/browse/JDK-8244576

[2] - http://cr.openjdk.java.net/~herrick/8244576/webrev.01/

/Andy