cron package is missing on ubuntu 16.04

[doka]

Cron is not installed by default in ubuntu:16.04 image. See this comment on Serverfault.

Hostmaster install ends with crontab error if using any Dockerfiles based on ubuntu:16.04

This command will replace your crontab for this user. continue? (y/n): y
/usr/bin/env php /usr/local/bin/drush '@hostmaster' hosting-dispatch
Dispatch command was run successfully                                [success]
No existing crontab was found                                          [message]
Adding hosting-dispatch cron entry to run every minute               [ok]
sh: 1: crontab: not found
Failed to install cron job                                           [error]
The command did not complete successfully, please fix the issues and [error]
re-run this script