Make network resource creation in isolation configurable

This commit adds a helper method to the base test class
set_network_resources(). This method should be called before the super
call in setUpClass and lets you specify which network resources
are created for a test class in tenant isolation. This is useful for
fine tuning each test class so that only the resources that are needed
get created.

Change-Id: I8f66534dbe3f48552ed6cd238ad237c46d7ee60c
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 409fcc2..2b5a770 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -235,7 +235,8 @@
     def setUpClass(cls):
         super(OfficialClientTest, cls).setUpClass()
         cls.isolated_creds = isolated_creds.IsolatedCreds(
-            __name__, tempest_client=False)
+            __name__, tempest_client=False,
+            network_resources=cls.network_resources)
 
         username, password, tenant_name = cls.credentials()