MIgrate to puppet 4

"Puppet 3 will reach end-of-life at the end of this year":https://puppet.com/misc/puppet-enterprise-lifecycle

We need to upgrade before this in order to not be left without security updates (even though the attack vector is smaller for us compared with a puppetmaster install).

(from redmine: created on 2016-10-26, relates #7983, relates #8135 (closed), relates #8183)