Retry seed loading in case snap is not ready yet (#925)

tests/integration/tests/test_util/harness/lxd.py

@@ -131,8 +131,11 @@ def new_instance(self, network_type: str = "IPv4") -> Instance:
         except subprocess.CalledProcessError as e:
             raise HarnessError(f"Failed to create LXD container {instance_id}") from e
 
-        self.exec(instance_id, ["snap", "wait", "system", "seed.loaded"])
-        return Instance(self, instance_id)
+        instance = Instance(self, instance_id)
+        stubbornly(retries=3, delay_s=5).on(instance).exec(
+            ["snap", "wait", "system", "seed.loaded"]
+        )
+        return instance
 
     def _configure_profile(self, profile_name: str, profile_config: str):
         LOG.debug("Checking for LXD profile %s", profile_name)