RFR: JDK-8214566 : --win-dir-chooser does not prompt if destination folder is not empty

[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).

- Added custom action to check installation folder and display 
confirmation dialog to ask user to continue installation if destination 
folder is not empty. This is same behavior and confirmation message as 
for .exe.

[1] https://bugs.openjdk.java.net/browse/JDK-8214566

[2] http://cr.openjdk.java.net/~almatvee/8214566/webrev.00/

Thanks,
Alexander