Comment 5 for bug 2056160

The UI is waiting until subiquity reports a state other than STARTING_UP, CLOUD_INIT_WAIT, or EARLY_COMMANDS. Apparently this was added as a fix for this: https://bugs.launchpad.net/subiquity/+bug/1988042 .

This is done before the Flutter app is drawn onto the screen, which is why only the empty GTK window is visible at this point. We'll need to refactor ubuntu-desktop-provision's initialization routine to be able to show a loading screen.