Implement Cinder Volume driver for HGST Solutions

Implement Cinder Volume driver for HGST Solutions

Enables native support for HGST Solutions software Spaces as
Cinder volumes or snapshots.

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.

Prerequisites:
HGST Solutions is a software-SAN-like package which allows local
SSDs in a cluster to be combined into a single storage pool.
The driver has a series of configuration options which must be set
in the cinder.conf, prefixed with hgst_*.
Nodes should have the HGST software installed and connected to the
HGST domain prior to rolling out Nova nodes using this storage.

Additional patches required for full functionality (being tracked
under the same blueprint):
OS-brick patch @ https://review.openstack.org/#/c/186588/
Nova patch @ https://review.openstack.org/#/c/186594/
Nova patch required until os-brick<->nova connection finalized
in https://review.openstack.org/#/c/175569/

Change-Id: Ie0ff03856edd4b5610f4412951ea7c970ad63c8c
Implements: blueprint add-volume-driver-hgst-solutions