Refactor local and raw parameters

Move each into a sub-group and fix all the related naming.

Adds a schema migration.
Don't keep raw and local 'volume_name' in sync

With multi-backend, they have to be different anyway.
Fix volume type locales

Use consistent naming and load all volume types from locale catalog.
Remove default[:cinder][:volume][:nfs_shares]

And use the hard-coded value '/etc/cinder/nfs_shares' that is also the
OpenStack default for both 'nfs' and 'nexenta' drivers. It would
otherwise conflict with multi-backend config values, which will reside
under node[:cinder][:volume]. Later, the file name will be fixed but
include the backend name, e.g. '/etc/cinder/nfs_shares-default' for the
'default' backend...
Remove default[:cinder][:volume][:rbd][:ceph_conf]

And hardcode '/etc/ceph/ceph.conf'. Not used at the moment. It's likely
that the ceph config file will be per-backend and thus include the
backend name, .e.g., '/etc/ceph/ceph-default.conf' for the 'default'
backend.
Add multi-backend support

Use multi-backend style configuration even if only one backend is set.

Include a migration.
Add 'volume_backend_name' for cinder backends

Can be used to influence scheduler decisions. For instance, when having
three backends, two could share the same volume_backend_name 'foo'. The
capacity filter scheduler would then choose the most suitable driver for
'foo' backend requests.