Front-end only deployment

[vholer]

While it's super useful to be able to deploy all-in-one evaluation environment, for the DDC scenario, it might be good to easily deploy only front-end and leave the hypervisor nodes on user or oneprovision tool.

Let's introduce parameter --frontend (or similar) to do only steps necessary to prepare a front-end (repositories, packages, install_gems, reconfiguration, initial user) and finish. No datastores, networks, image import, ...