Create only necessary resources for image, object_storage, volume

This patch leverages the set_network_resources method for
tempest test api of image, object_storage, volume.

Change-Id: I52f721285a9c07f4279b8320320baa3e21b09a51
diff --git a/tempest/api/image/base.py b/tempest/api/image/base.py
index 91f725e..5840c04 100644
--- a/tempest/api/image/base.py
+++ b/tempest/api/image/base.py
@@ -31,6 +31,7 @@
 
     @classmethod
     def setUpClass(cls):
+        cls.set_network_resources()
         super(BaseImageTest, cls).setUpClass()
         cls.created_images = []
         cls._interface = 'json'