snaplist: do not automatically mark configured on failed GET request

When a client sends a GET /snaplist request and an error occurs on the
server side, we return a response of the following form:

 { "status": "FAILED", ... }

This effectively gives a chance to the client to retry the same request
and expect a different outcome (for instance when a temporary network
failure occurs).

Having said that, when the server returns "status": "FAILED", it also
automatically marks the snaplist model configured. This is wrong because
if the next GET /snaplist request succeeds, the user will be prompted to
select some snaps to install ; but the installation will already be
running in the background. Depending on the timing, it might or might
not install the snaps that the user selected.

Fixed by not marking the snaplist model configured automatically. The
client is made responsible from sending a POST /snaplist ; even in case
of error.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/server/controllers/snaplist.py

@@ -170,13 +170,11 @@ class SnapListController(SubiquityController):
 
     async def GET(self, wait: bool = False) -> SnapListResponse:
         if self.loader.failed or not self.app.base_model.network.has_network:
-            await self.configured()
             return SnapListResponse(status=SnapCheckState.FAILED)
         if not self.loader.snap_list_fetched and not wait:
             return SnapListResponse(status=SnapCheckState.LOADING)
         await self.loader.get_snap_list_task().wait()
         if self.loader.failed or not self.app.base_model.network.has_network:
-            await self.configured()
             return SnapListResponse(status=SnapCheckState.FAILED)
         return SnapListResponse(
             status=SnapCheckState.DONE,