Allow to not have keys in etcd

uncloud/settings/__init__.py

@@ -115,7 +115,13 @@ class Settings(object):
             )
 
     def __getitem__(self, key):
-        self.read_values_from_etcd()
+        # Allow failing to read from etcd if we have
+        # it locally
+        try:
+            self.read_values_from_etcd()
+        except KeyError as e:
+            pass
+
         return self.config_parser[key]