pytest: Add test for sudo: search with lower cased name for case insensitive domains
    
    1. Add test case for sudo: search with lower
       cased name for case insensitive domains
    
    2. Add fixtures:
        disable case_sensitive
        enable sudo service
        add suders: sss in nsswitch.conf
    
    Signed-off-by: Niranjan M.R <mrniranjan@redhat.com>
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>