Here is a sample configuration section that you can put in
/etc/jailkit/jk_init.ini so that future jail adds are seamless.
I used this section
comment = mysql client
executables = /usr/bin/mysql
paths = /usr/lib/libmysqlclient.so.16.0.0 , /usr/lib/libmysqlclient.so.16, /usr/lib/libstdc++.so.6,/usr/lib/libstdc++.so.6.0.13,/lib/libgcc_s.so.1
Seemed to work well, you may need to change some paths. jailkit MAY resolve the symlink paths on its own but i added both in case.
1) Users must use full mysql -h syntax (mysql -h basehostname database) since you do not have the mysql local sockets in the jail
2) Your mysql must be listening on the public interface so the jail can connect to it.