Fix regression introduced by proxy port.

bin/cros_run_vm_update

 #!/bin/bash
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # Updates an existing vm image with another image.
 
 . "$(dirname $0)/../common.sh"
 . "$(dirname $0)/../lib/cros_vm_lib.sh"
@@ skipping 23 matching lines @@
 
 if [ -n "${FLAGS_update_image_path}" ]; then
   IMAGE_ARGS="--image=$(readlink -f ${FLAGS_update_image_path})"
 fi
 
 if [ -n "${FLAGS_payload}" ]; then
   IMAGE_ARGS="--payload=${FLAGS_payload}"
 fi
 
 if [ -n "${FLAGS_proxy_port}" ]; then
-  IMAGE_ARGS="--proxy_port=${FLAGS_proxy_port}"
+  IMAGE_ARGS="${IMAGE_ARGS} --proxy_port=${FLAGS_proxy_port}"
 fi
 
 $(dirname $0)/../image_to_live.sh \
   --remote=127.0.0.1 \
   --ssh_port=${FLAGS_ssh_port} \
   --stateful_update_flag=${FLAGS_stateful_update_flag} \
   --src_image="${FLAGS_src_image}" \
   --verify \
   --for_vm \
   ${IMAGE_ARGS}