Create a Cinder Volume driver for HGST Solutions clustered flash software

Add a Cinder Volume backend driver to support HGST Solutions software, as well as os-brick connectors. This driver will use HGST Solutions software to provide a stable, shared, highly available, and high performance store for Cinder volumes on distributed local SSD storage.

The driver should support all required minimum features for Liberty (L) release.

HGST Solutions is a software-SAN-like package which allows local SSDs in a cluster to be combined into a single storage pool. This pool can then be carved into HA (mirror-replicated) "Spaces" which can be managed/accessed from any member of the cluster.

Each Cinder Volume or Snapshot is mapped to a single HGST Space. This space may be named differently from the actual volume/snap ID and so we store the Space Name<->ID mapping in the volume provider_id. Snapshots are not supported with the current HGST Solutions software, so they are implemented as heavyweight copies in the driver.

All Spaces are made visible on the Cinder host for speed of access, and only the spaces requested by Nova instances are actually made visible on other members of the cluster.

Not all nodes need SSD storage to take advantage of these volumes, cinder.conf entries specify which nodes share their local SSDs.