Set USE_SSL to 0 for testing_ssl
mysql> update mysql_users set use_ssl=0 where username='testing_ssl'
    -> ;
Query OK, 1 row affected (0.00 sec)

mysql> LOAD MYSQL SERVERS TO RUNTIME;
Query OK, 0 rows affected (0.01 sec)

mysql> LOAD MYSQL USERS TO RUNTIME;
Query OK, 0 rows affected (0.00 sec)

[root@xxxxxxxxxxx ~]# mysql -h172.18.153.161 -utesting_ssl -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.1.30 (ProxySQL)

Copyright (c) 2009-2015 Percona LLC and/or its affiliates
Copyright (c) 2000, 2015, 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> \s
--------------
mysql  Ver 14.14 Distrib 5.6.23-72.1, for Linux (x86_64) using  EditLine wrapper

Connection id:		3
Current database:	information_schema
Current user:		testing_ssl@172.18.153.161
SSL:			Not in use
Current pager:		stdout
Using outfile:		''
Using delimiter:	;
Server version:		5.1.30 (ProxySQL)
Protocol version:	10
Connection:		172.18.153.161 via TCP/IP
Server characterset:	latin1
Db     characterset:	utf8
Client characterset:	utf8
Conn.  characterset:	utf8
TCP port:		3306
Uptime:			10 min 37 sec

Threads: 1  Questions: 6  Slow queries: 0
--------------

mysql> show processlist;
+------+-------------+----------------------+--------------------+---------+------+-------+------------------+-----------+---------------+
| Id   | User        | Host                 | db                 | Command | Time | State | Info             | Rows_sent | Rows_examined |
+------+-------------+----------------------+--------------------+---------+------+-------+------------------+-----------+---------------+
|    3 | root        | localhost            | NULL               | Sleep   |    3 |       | NULL             |         0 |             0 |
|   38 | monitoring  | localhost            | NULL               | Sleep   |    4 |       | NULL             |         0 |             0 |
|   42 | monitoring  | localhost            | NULL               | Sleep   |   59 |       | NULL             |       403 |           403 |
|   63 | monitoring  | localhost            | NULL               | Sleep   |   22 |       | NULL             |         0 |             0 |
| 2908 | monitor     | 172.18.153.161:38034 | NULL               | Sleep   |    0 |       | NULL             |         0 |             0 |
| 3183 | testing     | 172.18.153.161:38835 | information_schema | Sleep   |    5 |       | NULL             |         0 |             0 |
| 3232 | testing_ssl | 172.18.153.161:39006 | information_schema | Query   |    0 | init  | show processlist |         0 |             0 |
| 3240 | root        | localhost            | information_schema | Sleep   |   21 |       | NULL             |         1 |             5 |
+------+-------------+----------------------+--------------------+---------+------+-------+------------------+-----------+---------------+
8 rows in set (0.02 sec)


mysql> select * from USER_STATISTICS where user ='testing_ssl'\G
*************************** 1. row ***************************
                  USER: testing_ssl
     TOTAL_CONNECTIONS: 1
CONCURRENT_CONNECTIONS: 0
        CONNECTED_TIME: 144
             BUSY_TIME: 0
              CPU_TIME: 0
        BYTES_RECEIVED: 294
            BYTES_SENT: 0
  BINLOG_BYTES_WRITTEN: 0
          ROWS_FETCHED: 21
          ROWS_UPDATED: 0
       TABLE_ROWS_READ: 63
       SELECT_COMMANDS: 4
       UPDATE_COMMANDS: 0
        OTHER_COMMANDS: 4
   COMMIT_TRANSACTIONS: 0
 ROLLBACK_TRANSACTIONS: 0
    DENIED_CONNECTIONS: 0
      LOST_CONNECTIONS: 1
         ACCESS_DENIED: 0
         EMPTY_QUERIES: 0
 TOTAL_SSL_CONNECTIONS: 1

Check out TOTAL_SSL_CONNECTIONS: 1 when use_ssl was disabled.

After that I enabled it back,
mysql> update mysql_users set use_ssl=1 where username='testing_ssl'
    -> ;
Query OK, 1 row affected (0.00 sec)

mysql> LOAD MYSQL SERVERS TO RUNTIME;
Query OK, 0 rows affected (0.00 sec)

mysql> LOAD MYSQL USERS TO RUNTIME;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from mysql_users;
+-------------+----------+--------+---------+-------------------+----------------+---------------+------------------------+--------------+---------+----------+-----------------+
| username    | password | active | use_ssl | default_hostgroup | default_schema | schema_locked | transaction_persistent | fast_forward | backend | frontend | max_connections |
+-------------+----------+--------+---------+-------------------+----------------+---------------+------------------------+--------------+---------+----------+-----------------+
| testing     | xxxxx    | 1      | 0       | 2                 | NULL           | 0             | 0                      | 0            | 1       | 1        | 10000           |
| testing_ssl | xxxxx     | 1      | 1       | 1                 | NULL           | 0             | 0                      | 0            | 1       | 1        | 10000           |
| test1       | xxxxx    | 1      | 0       | 0                 | NULL           | 0             | 0                      | 0            | 1       | 1        | 10000           |
+-------------+----------+--------+---------+-------------------+----------------+---------------+------------------------+--------------+---------+----------+-----------------+
3 rows in set (0.00 sec)

# mysql -h172.18.153.161 -utesting_ssl -p
Enter password:
ERROR 1045 (#2800): Access denied for user 'testing_ssl' (using password: YES)