MySQL turns off password strength verification

[root@mysql mysql]# mysql -uroot -p123456 
mysql: [Warning] Using a password on the command line interface can be insecure. 
Welcome to the MySQL monitor. Commands end with ; or \g. 
Your MySQL connection id is 4 
Server version: 5.7.18 
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved. 
Oracle is a registered trademark of Oracle Corporation and/or its 
affiliates. Other names may be trademarks of their respective 
owners. 
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 
mysql>  
mysql>  
mysql> use mysql 
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement. 
mysql> SET PASSWORD = PASSWORD(''); 
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements 
mysql> exit 
Bye 
[root@mysql mysql]#  
[root@mysql mysql]#  
[root@mysql mysql]# vi /etc/my.cnf 
# For advice on how to change settings please see 
# http://dev.mysql.com/doc/refman/5.7/en/server-configuration-defaults.html 
[mysqld] 
# 
# Remove leading # and set to the amount of RAM for the most important data 
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%. 
# innodb_buffer_pool_size = 128M 
# 
# Remove leading # to turn on a very important data integrity option: logging 
# changes to the binary log between backups. 
# log_bin 
# 
# Remove leading # to set options mainly useful for reporting servers. 
# The server defaults are faster for transactions and fast SELECTs. 
# Adjust sizes as needed, experiment to find the optimal values. 
# join_buffer_size = 128M 
# sort_buffer_size = 2M 
# read_rnd_buffer_size = 2M 
datadir=/var/lib/mysql 
socket=/var/lib/mysql/mysql.sock 
# Disabling symbolic-links is recommended to prevent assorted security risks 
symbolic-links=0 
log-error=/var/log/mysqld.log 
pid-file=/var/run/mysqld/mysqld.pid 
plugin-load=validate_password.so 
validate-password=OFF 
~ 
~ 
~ 
~ 
~ 
~ 
~ 
~ 
"/etc/my.cnf" 30L, 1016C written 
[root@mysql mysql]# service mysqld restart 
Stopping mysqld: [ OK ] 
Starting mysqld: [ OK ] 
[root@mysql mysql]# mysql -uroot -p123456 
mysql: [Warning] Using a password on the command line interface can be insecure. 
Welcome to the MySQL monitor. Commands end with ; or \g. 
Your MySQL connection id is 4 
Server version: 5.7.18 
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved. 
Oracle is a registered trademark of Oracle Corporation and/or its 
affiliates. Other names may be trademarks of their respective 
owners. 
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 
mysql>  
mysql>  
mysql> use mysql 
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement. 
mysql> SET PASSWORD = PASSWORD(''); 
Query OK, 0 rows affected, 1 warning (0.00 sec) 
mysql>