Introduction
There is no easy way to rotate or clear error_log files that grow to a certain size.
Procedure
This can be either done in a user's cron job with the path to the user's home directory or can be done on the entire data path for users on the server like /home.
The following example would be to add into root's crontab to clear users error_log files over 2M in size.
find /home -path /home/virtfs -prune -false -o -type f -size 2M -name error_log -exec rm -f '{}' \;