RFR: JDK-8231604: Expand junit test added with JDK-8230920

[Andy Herrick]

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).

Simple junit test addition to cover add-launchers in AppInfoFile.

/Andy

[1] https://bugs.openjdk.java.net/browse/JDK-8231604

[2] http://cr.openjdk.java.net/~herrick/8231604/webrev.01/