This patch implements cinder Replication version 2.1 as proposed in
https://blueprints.launchpad.net/cinder/+spec/replication
The driver implements:
1. freeze_backend - notify the backend that it's frozen
2. thaw_backend - notify the backend that it's not frozen
3. host_failover - failover a backend to a secondary replication target
Also removed v1.0 and v2.0 functions
DocImpact
Change-Id: I50498180c63725ab0f524ff8d55952446800570f
Closes-Bug: #1543600