RFR: JDK-8222676: create-installer with --app-image fails on mac

[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).

- Fixed issue when app image is located at root of working folder, since 
fix for JDK-8219144 assumed app image located under some folder other 
then working directory.
- Another issue found while working on this bug: pkgbuild will package 
any components in root folder or any sub-folder, so app image should be 
only one component in root folder without any sub-folder. This issue is 
fixed by making copy of app image if it is located in folder with other 
files.

[1] https://bugs.openjdk.java.net/browse/JDK-8222676

[2] http://cr.openjdk.java.net/~almatvee/8222676/webrev.00/

Thanks,
Alexander