triggers: Use FlatpakBwrap helpers
triggers: Use FlatpakBwrap helpers

This makes the code cleaner and more flexible for changes later.

Closes: #2755
Approved by: alexlarsson

matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak