cinder-backup: Ensure ca cert is defined when tls-proxy is enabled

Change-Id: Id679eb7061d8e609ce76fbb5b720a041990e8e86
diff --git a/lib/cinder_backups/swift b/lib/cinder_backups/swift
index d7c977e..c7ec306 100644
--- a/lib/cinder_backups/swift
+++ b/lib/cinder_backups/swift
@@ -24,6 +24,9 @@
     # to use it.
     iniset $CINDER_CONF DEFAULT backup_driver "cinder.backup.drivers.swift.SwiftBackupDriver"
     iniset $CINDER_CONF DEFAULT backup_swift_url "$SWIFT_SERVICE_PROTOCOL://$SERVICE_HOST:$SWIFT_DEFAULT_BIND_PORT/v1/AUTH_"
+    if is_service_enabled tls-proxy; then
+        iniset $CINDER_CONF DEFAULT backup_swift_ca_cert_file $SSL_BUNDLE_FILE
+    fi
 }
 
 # init_cinder_backup_swift: nothing to do