Add support for cinder consistency groups

Add support for Cinder consistency groups to the Project -> Volumes panel

Motivation:

Consistency groups were added to Cinder in Juno. Consistency groups are used to group volumes
together for the purpose of data protection (snapshots, backups) and disaster recovery. Cinder
currently supports creating snapshots across a consistency group, and is planning for additional
functionality (backups, etc.) in upcoming releases.

This change will expose the following cinder CLI commands in the UI:

Consistency group management:
- cinder consisgroup-create
- cinder consisgroup-delete
- cinder consisgroup-list
- cinder consisgroup-show

Consistency group snapshot:
- cinder cgsnaptoh-create
- cinder cgsnaptoh-delete
- cinder cgsnaptoh-list
- cinder cgsnaptoh-show

UX:
Create a new Consistency Group tab in the "Project -> Volumes". It will have a table listing all
consistency groups, with a table action for Create and a row action for Delete. The name will be a link to
the details page. A new Consistency Group Snapshot tab will have be similar, with a table of snapshots and
actions for creation and deletion.

Outside Dependencies:
The cinder changes to support consistency groups and their snapshots were introduced in Juno, and
are present in the cinder v2 API. Additional improvements are being made in Kilo, including
See also https://blueprints.launchpad.net/cinder/+spec/consistency-groups-kilo-update.

Requirements Update Required:
N/A

Doc Impact:
N/A