We've been performing MySQL 5.6 to 5.7 upgrades for some of our clients.
In MySQL 5.6 the --log-error is passed on the command line when MySQL is started. With MySQL 5.7 it's missing. I can see in the /etc/my.cnf.rpmnew file that there is a log-error=/var/log/mysqld.log set, but the upgrade is not merging that into /etc/my.cnf so it's not getting set.
On servers that just had MySQL 5.7 installed I can see the line in /etc/my.cnf, so this "seems" like a bug?

# mysql -e "show variables" | egrep log_error
binlog_error_action     ABORT_SERVER
log_error       stderr
log_error_verbosity     3

I created a CentOS 7 machine, specified that I wanted MySQL 5.6 on it, ran the cPanel installer, performed an upgrade to MySQL 5.7, and I confirmed the issue.
I've created a case with our developers so they can look into this a bit more and I'll post an update here once I have one.

@ffeingol - our devs did some more testing with this and found this is the default value included with MySQL 5.7, so you're just seeing the default value change.
If the value is applied to /etc/my.cnf, that gets retained during the update, but the change isn't something special we're doing on the cPanel side of things as that's all handled with the MySQL upgrade process.

Ok, then this doc needs to be updated: The cPanel & WHM Log Files | cPanel & WHM Documentation with a qualifier that it will be in /var/log/mysql.log if you did a fresh install of MySQL 5.7, but if you upgrade, it wont' be there ;-)
We'll just add:
Code:

log-error=/var/log/mysqld.log