UTIL: Add sss_filter_sanitize_ex
    
    Related:
        https://fedorahosted.org/sssd/ticket/2553
    
    In order to support wildcard request, we need to introduce an optionally
    relaxed version of sss_filter_sanitize that allows to select which
    characters are exempt from sanitizing.
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>