RFR: JDK-8230651: Use version string from main module

[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).

- Version from main module (if exist) will be used as --app-version if 
--app-version is not specified.

[1] https://bugs.openjdk.java.net/browse/JDK-8230651

[2] http://cr.openjdk.java.net/~almatvee/8230651/webrev.01/

Thanks,
Alexander