Remove host option

Update cinder backend config for ceph,
backend parameter "host" has been deprecated starting from Kilo,
and changed to "backend_host", and, since Pike, it was removed
completely.

Change-Id: I7c20d6cfd32fa37c9bfe33d0938f71e5afb73c64
Related-Prod: PROD-22192 (PROD:22192)
3 files changed