Add a playbook to rerun install_puppet.sh with PUPPET_VERSION=4. Also
make the install_modules.sh script smarter about figuring out the puppet
version so that the update_puppet.yaml playbook, which updates the
puppet config and puppet modules but not the puppet package, does not
need to be changed.
When we're ready to start upgrading nodes, we'll add them to the puppet4
group in `modules/openstack_project/files/puppetmaster/groups.txt`.
Change-Id: Ic41d277b2d70e7c25669e0c07e668fb9479b8abf