tests: Skip two more tests when bwrap is missing
tests: Skip two more tests when bwrap is missing

This adds the logic from test_install_launch_uninstall() to
test_instance() and test_overrides() so that all three are skipped in CI
environments where bwrap may not be working. This is necessary because
they all use flatpak_installation_launch().

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