Split cinder_storage class

The cinder_storage class served two different purposes:

* mounting of Gluster volumes into controller,

* providing a LVM block storage backend accessible through iSCSI.

Mounting of Gluster volumes has moved into cinder_controller, and the
LVM block storage backend has moved into
storage_backend::lvm_cinder. The cinder_storage class has been
removed.
Host groups: update LVM storage, add Gluster

Host group for LVM storage has been updated to reflect the class move
and a new host group for Gluster storage backend (general for Cinder,
Glance, Swift in the future) has been added.
Cascade parameters from storage_backend::gluster

We need to pass parameters needed for storage_backend::gluster::cinder
and storage_backend::gluster::glance into storage_backend::gluster (top
class for Gluster Storage host group), because we want Foreman to
override them, instead of inheriting values from quickstack::params.
Merge pull request #46 from jistr/gluster_pt1

Gluster part 1