RFR: JDK-8233244: Add tests for icons configuration in rpm/deb packages

[Alexey Semenyuk]

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

The fix adds verification there are `xdg-icon-resource` commands in 
Linux packages for file associations with icons.

- Alexey

[1] https://bugs.openjdk.java.net/browse/JDK-8233244

[2] http://cr.openjdk.java.net/~asemenyuk/8233244/webrev.00