Upgrade Puppet master and clients to 3.8

That’s one recommended step towards migrating to Puppet 4, e.g. so that agents can connect to a v4 puppetmaster: https://docs.puppet.com/puppet/4.5/reference/upgrade_major_pre.html#update-to-the-latest-puppet-server-11x-puppet-38x-and-puppetdb-23x.

Parent Task: #11834 (closed)

Related issues

Blocks #11836 (closed)
Blocks #11833 (closed)

Original created by @intrigeri on 11835 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information