mark the locale model as configured at start up

The subiquity client does not ask about language in non-rich mode on a
serial port, and that's OK. But we still need the install to complete :)

There are other ways to fix this I guess -- we could not wait on the
locale model to get configured, for example, or explicitly select a
C.UTF-8 locale when "Continue in basic mode" is selected, or probably
some other things. But this works and seems OK.

subiquity/server/controllers/locale.py

@@ -36,6 +36,7 @@ class LocaleController(SubiquityController):
 
     def start(self):
         self.model.selected_language = os.environ.get("LANG")
+        self.configured()
 
     def serialize(self):
         return self.model.selected_language