Use the $SERVICE_HOST in backup_swift_url

The $SERVICE_HOST is used to specify the swift proxy endpoint,
the c-bak should use the same endpoint.

Change-Id: Ia815f514839b0d1ec3fb9bb40992637c4f123e06
diff --git a/lib/cinder b/lib/cinder
index dd2956a..dadbe40 100644
--- a/lib/cinder
+++ b/lib/cinder
@@ -274,6 +274,10 @@
     iniset $CINDER_CONF DEFAULT lock_path $CINDER_STATE_PATH
     iniset $CINDER_CONF DEFAULT periodic_interval $CINDER_PERIODIC_INTERVAL
 
+    if is_service_enabled swift; then
+        iniset $CINDER_CONF DEFAULT backup_swift_url "http://$SERVICE_HOST:8080/v1/AUTH_"
+    fi
+
     if is_service_enabled ceilometer; then
         iniset $CINDER_CONF DEFAULT notification_driver "cinder.openstack.common.notifier.rpc_notifier"
     fi