RFR: 8233166: jpackage tool skips empty directories

[Alexander Matveev]

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

- Fixed code which enumerates folders and files to include empty folders.
- Added EmptyFolderTest.

[1] https://bugs.openjdk.java.net/browse/JDK-8233166

[2] http://cr.openjdk.java.net/~almatvee/8233166/webrev.00/

Thanks,
Alexander