pybridge: Fix superuser startup vs. package reloading race

When the superuser bridge gets auto-started via the init message or the
integration tests, it can happen that loading the packages and manifests
finishes after the superuser bridge already runs. That bridge previously
had the name "init", and once packages finished loading, set_config()
stopped that "init" bridge as it is not decleared by the manifests
(usually "sudo" and "pkexec"). That led to the session sometimes not
being privileged.

This was particularly prone to happen in the "devel" scenario where the
packages are much larger and processing took much longer.

Avoid that by setting `self.current` to the correct requested name right
from the start.

Fixes #19014

src/cockpit/superuser.py

@@ -168,19 +168,19 @@ async def go(self, name: str, responder: ferny.InteractionResponder) -> None:
         except KeyError as exc:
             raise bus.BusError('cockpit.Superuser.Error', f'Unknown superuser bridge type "{name}"') from exc
 
-        self.current = 'init'
+        self.current = name
         self.peer = SuperuserPeer(self.router, config, responder)
         self.peer.add_done_callback(self.peer_done)
 
         try:
             await self.peer.start(init_host=self.router.init_host)
         except asyncio.CancelledError:
+            self.current = None
             raise bus.BusError('cockpit.Superuser.Error.Cancelled', 'Operation aborted') from None
         except (OSError, PeerError) as exc:
+            self.current = None
             raise bus.BusError('cockpit.Superuser.Error', str(exc)) from exc
 
-        self.current = name
-
     def set_configs(self, configs: List[Dict[str, object]]):
         logger.debug("set_configs() with %d items", len(configs))
         self.superuser_configs = {}