Upgrade all lizard VMs to Jessie

Originally created by @intrigeri on #11186 (Redmine)

Expected outcome:

• (with tails/sysadmin#11178): drop Wheezy special cases from our Puppet code
• don’t have to go through Wheezy -> Stretch upgrade (yes, there will be wheezy-lts but I suspect this upgrade path will be less well tested than Wheezy -> Jessie + Jessie -> Stretch)
• be able to rely on having systemd everywhere

Related issues

• Related to tails/sysadmin#11178
• Related to tails/sysadmin#11184