Set same hostname for each cinder-volume for Ceph backend.

Change-Id: I1e76a935286d48c4c449c14bef7d8eeb279fc01a
diff --git a/cinder/control/backend/ceph.yml b/cinder/control/backend/ceph.yml
index 1026f68..3b036d4 100644
--- a/cinder/control/backend/ceph.yml
+++ b/cinder/control/backend/ceph.yml
@@ -11,3 +11,4 @@
           user: ${_param:cinder_storage_user}
           secret_uuid: ${_param:cinder_storage_secret_uuid}
           client_cinder_key: ${_param:cinder_storage_client_key}
+          host: ceph