role: add classes to configure Ceph clusters through simple ENCs

These classes add the ability to configure MONs and OSDs through the exclusive use of un-parameterized classes, global and node variables. This allows users to configure a Ceph cluster with even a simple ENC such as Puppet Dashboard (or a home-rolled ENC), or by greatly simplified site manifests that are essentially a few variable definitions plus some includes.

An example site manifest, providing identical functionality to the one defined in the currently shipped example site.pp, is also included.

MDS and radosgw configuration still require some extra work in the low-level classes.