Install puppetdb-terminus on base box with the puppetlabs repo #4

This way we're ready to apply a puppet config without requiring any
further bootstrapping of sources.
Add the puppetlabs key and repo before running apt-get update
Install puppetdb-terminus as part of the base-packages

This way we don't run `apt-get update` more than once.
Add an admin group, part of #4
Install bundler as part of base packages, fixes #4