unskip test_security_group_rules_negative tests

Neutron validates the uuid format as nova the integer format,
 so if we want 404 for non existent, resource we need to use a valid uuid.

Change-Id: I80f5b9a8f2bc75f8b9c3ba753070ee6f5ea44f5e
Merge "unskip test_security_group_rules_negative tests"