Improve Cinder API internal cache interface

Improve the internal caching system used by the API layer
by borrowing the implementation used by Nova.

Unlike the previous implementation, this new interface makes it clear
which resource types are added or retrieved from the cache.

This change also adds other resources to the cache:
- backups
- snapshots
- volume types

It's now possible to remove database access those extensions:
- extended_snapshot_attributes
- volume_host_attribute
- volume_mig_status_attribute
- volume_tenant_attribute

Closes-bug: #1358524
Change-Id: I1fc673d0c01c41faa98292d5813d4471b455d712
Merge "Improve Cinder API internal cache interface"