If you encounter a situation where you can't create a new site after WO update, but you can access mysql as root without typing any password, here goes a dirty fix that worked for me.
Everything below is supposed to be run by root.
First, ensure there is a .my.cnf
in your root:
cp /etc/mysql/conf.d/my.cnf /root/.my.cnf
Now, show the default root password:
grep password /root/.my.cnf | awk '{print $3}'
Take note of this password. Let's pretend it is "abcdef1234".
Now, enter MySQL:
mysql
In MySQL prompt type:
use mysql
ALTER USER 'root'@'localhost' IDENTIFIED BY 'abcdef1234';
flush privileges;
exit
Of course, replace the fake password above with the password you noted before.
That's it. After this your WO should be able to properly create new sites.