intg: convert results returned as bytes to strings
    
    With python3 comparisons between byte literals and strings will fail. To
    make sure assertions will pass the search results must be converted to
    (utf-8) strings first.
    
    Resolves https://pagure.io/SSSD/sssd/issue/3666
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>