tests: Print spawned program argv in testlibrary
tests: Print spawned program argv in testlibrary

This makes debugging failures a little easier.

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,flatpak/flatpak