Stop stringifying Puppet facts

Originally created by @intrigeri on #11836 (Redmine)

That’s one of the steps of the migration to Puppet 4: https://docs.puppet.com/puppet/4.5/reference/upgrade_major_pre.html#stop-stringifying-facts-and-check-for-breakage

Parent Task: tails/sysadmin#11834

Related issues

• Blocks tails/sysadmin#11837
• Blocked by tails/sysadmin#11835
• Blocks tails/sysadmin#11833