- Tolerate situation, when datadir for service seems invalid/non-existing
prior to upgrade. It could be that my.ini contains legacy ANSI characters
for the data directory. Those can't be read correctly by
mysql_upgrade_service, which uses a different ANSI codepage(UTF8)
.
- schedule upgrade_config_file at later stage, because once we
convert it to UTF-8 (followup patch), this will render config file uselss
with the older version of mariadbd.exe

- Refactor upgrade_conf_file.cc, prepare for UTF-8 conversion.