Use sysupdate images

#66 (closed)

Current status:

• Tests load and run successfully, pipeline https://gitlab.gnome.org/GNOME/openqa-tests/-/pipelines/601781 completed in 14m33s.
• Some app tests fail:
  • app_gnome_console: hostname is 'localhost' rather than 'gnomeos'
  • app_baobab~~ and app_gnome_disk_utility because partition layout is different~~
• Fetching the 'latest' sysupdate image is fragile - see gnome-build-meta#766 (closed)
• Journal logs are not available, perhaps the smbios isn't working as it should