Comment 4 for bug 910566

This is still an issue on 14.04 where you'll need to hunt and install packages libcache-{perl,cache-perl} before the mysql_ plugin is satisfied.

At least this is noted by a suggests in the most recent package releases; https://launchpad.net/ubuntu/zesty/amd64/munin-plugins-core/2.0.33-1

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.3 LTS
Release: 14.04
Codename: trusty

$ munin-node-configure --suggest
Plugin | Used | Suggestions
------ | ---- | -----------
...
mysql_ | no | no [Missing dependency Cache::Cache]
...
$ apt install libcache-{perl,cache-perl}
...
$ munin-node-configure --suggest
Plugin | Used | Suggestions
------ | ---- | -----------
...
mysql_ | no | yes (+bin_relay_log +commands +connections +files_tables +innodb_bpool +innodb_bpool_act +innodb_insert_buf +innodb_io +innodb_io_pend +innodb_log +innodb_rows +innodb_semaphores +innodb_tnx +myisam_indexes +network_traffic +qcache +qcache_mem +replication +select_types +slow +sorts +table_locks +tmp_tables)
...