Fix oslo-config value substitution

Change-Id: I923b7dff56630339d3f73a28f5cb5898c608087d
diff --git a/tcp_tests/helpers/oslo_cfg_types.py b/tcp_tests/helpers/oslo_cfg_types.py
index aff8db0..f7be2d7 100644
--- a/tcp_tests/helpers/oslo_cfg_types.py
+++ b/tcp_tests/helpers/oslo_cfg_types.py
@@ -133,5 +133,5 @@
         res = super(Cfg, self)._get_from_namespace(namespace, group_name)
         # Use the value from enviroment variable instead of config
         if hasattr(self, 'environment_value'):
-            res = (self.environment_value, res[1])
+            res = self.environment_value
         return res