remote/exporter: flush messages regularly during exporter startup

Signed-off-by: Jan Luebbe <[email protected]>

labgrid/remote/exporter.py

@@ -777,6 +777,9 @@ async def run(self) -> None:
                     group_name, resource_name, cls, params
                 )
 
+            # flush queued message
+            await self.out_queue.join()
+
         logging.info("creating poll task")
         self.poll_task = self.loop.create_task(self.poll())