ldap: fix handling of binary data in search filters
    
    This fixes a UnicodeDecodeError when passing non-UTF-8 binary data to
    LDAPClient.make_filter() and friends.
    
    https://fedorahosted.org/freeipa/ticket/5381
    
    Reviewed-By: David Kupka <dkupka@redhat.com>
    Reviewed-By: Pavel Vomacka <pvomacka@redhat.com>