Harp should support Assemblies as a resource type.

We are defining assemblies as a combination of an instance (a base image) plus some post-book configuration by a DevOps tool (e.g. Puppet, Chef, etc.)

We should build a JSON definition of an assembly and a generic description of recipes/modules/etc. to run.

An assembly should support all of the currently supported devops types: Chef, Puppet, Ansible, Salt.
