Configure Cinder Volume service v2 endpoints

Updates the register-endpoint script so that it supports
configuring 'volumev2' endpoints. Also updates setup-endpoints
so that we configure both v1 and v2 Cinder endpoints in
the Keystone catalog for now.

This will help us transition to the new Cinder V2 endpoint.

Partial-bug: #1391603

Change-Id: Ic20d8df1d7bb559f6a2fe76f35c2e419477604eb