Make sure package_name is always set to a reasonable value

It's way easier to have a default we can rely on and override when required, rather than always needing to pass the variable.

The variable is required by kpkginstall for RPMs. The pipeline does not scream if the value is missing and kpkginstall gets quietly very unhappy. That situation should have never happened. Set the default and make sure the test generation screams if something goes horribly wrong and the value disappears.

Signed-off-by: Veronika Kabatova vkabatov@redhat.com