[build] only include specific props into izpack installer

[line-o]

forward port of #5723

[line-o]

I suspect that we listed a property that is unset.

[reinhapa]

@line-o just let it run with a IzPack 7.0.0 local development version and here are the properties where is no value available:

[WARNING] Specified property: project.build.target does not exist
[WARNING] Specified property: project.build.source does not exist
[WARNING] Specified property: jdom1.version does not exist

I suggest to remove those and it should work... (NPE within IzPack will be fixed in the upcoming major release)

[reinhapa]

@dizzzz any obligations of merging this?

[dizzzz]

Gogogo!