puppet/experimental: enable puppet4 jobs on xenial
puppet/experimental: enable puppet4 jobs on xenial

Puppetlabs packaged puppet4 on Xenial.
This patch adds the jobs in experimental queue so we can start testing
Puppet OpenStack on Xenial with Puppet4.

Change-Id: I8fa185fd96032c885ff8a0d3340b82c26023744f

Tesora/tesora-project-config,dongwenjuan/project-config,Tesora/tesora-project-config,openstack-infra/project-config,openstack-infra/project-config,dongwenjuan/project-config