intg: Add test for user and group local overrides
    
    Introduce a new integration test for local view overrides.
    
    Regression tests for: #2790, #2757 and #2802.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2732
    
    Reviewed-by: Nikolai Kondrashov <Nikolai.Kondrashov@redhat.com>