LDAP: sanitize group name when used in filter
    
    cleanup_groups() uses DN of group in filter for ldbsearch. But the name
    might contain characters with special meaning for filtering
    like - "*()\/"
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2744
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>