(PUP-1433) Add example environment to deb/rpm packages

This adds an /etc/puppet/environments/example_env directory,
subdirectories, and a README about the environment. We can't remove the
existing /etc/puppet/manifests directory because it would destroy a large
number of deployments (anyone with automation depending on that directory
being created). We also can't create a production environment because it
would then shadow the /etc/puppet/manifests directory and also end up
breaking automation as well as any existing regular installations. The
example environment with a README seems to be the best way to move forward
and try to present the new system to users.