sysdb: Use ldb_result as output in sysdb_search_ts_{users,groups}
    
    Passing address of unsigned to the output argument size_t causes
    access out of boundaries for type unsigned and and wrong data
    on big endian. It looks like functions sysdb_search_ts_{users,groups}
    need to store results in structure ldb_result anyway for further processing.
    Therefore it will be better to convert output arguments
    size_t* + ldb_message*** into structure ldb_result and avoid using
    additional helper variable with type size_t before each invocation
    of these functions.
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>