Integrate lunr block storage

The block storage service is being implemented as a separate project called lunr. This blueprint is for supporting and integrating that service into nova.

An API-fronted iSCSI-based block storage service that aims to offer moderate performance with a very low cost/GB of capacity. The service is composed in a 3-tier architecture.

1. Front-End API
2. Controller
2. Driver & Storage Subsystem

A basic description of each major component is described below:

Front-End API
 - Serves as the CRUD interface to consumers of storage
 - Request rate-limiting mechanisms are imposed here
 - List of API methods
   - Create Volume
   - List Volumes
   - List Performance of a Volume (IOPS)
   - List Usage of a Volume (I/O transactions aggregated over some time period)
   - Update Volume (metadata)
   - Delete Volume
   - Create Snapshot
   - List Snapshots
   - Update Snapshot (metadata)
   - Delete Snapshot

Controller
- Responsible for intelligent allocation and de-allocation of storage volumes across storage nodes
- Responsible for coordinating migration of volumes across storage nodes
- Responsible for coordination snapshot movement to/from Swift (Object Storage)
- Responsible for collecting IOPS metrics for performance and usage

Driver & Storage Subsystem
- Responsible for delivering a moderate level of performance and capacity
- Responsible as the target of an iSCSI session (a hypervisor would serve as the initiator)
- Responsible for generating IOPS metrics for performance and usage