Add vm flag to the devserver to not patch the kernel.  This is necessary for delta updates as vm images do not have patched kernels.

Change-Id: Ibd8325648febe84264d15e0d6c4d46820bfe5f96

BUG=8306
TEST=Ran it with cros_run_vm_update and with the --for_vm flag CL.

Review URL: http://codereview.chromium.org/4106009
diff --git a/devserver.py b/devserver.py
index 7a43530..4b98db3 100755
--- a/devserver.py
+++ b/devserver.py
@@ -116,6 +116,8 @@
                     default='MementoSoftwareUpdate')
   parser.add_option('--factory_config', dest='factory_config',
                     help='Config file for serving images from factory floor.')
+  parser.add_option('--for_vm', dest='vm', default=False, action='store_true',
+                    help='Update is for a vm image.')
   parser.add_option('--image', dest='image',
                     help='Force update using this image.')
   parser.add_option('-p', '--pregenerate_update', action='store_true',
@@ -161,7 +163,8 @@
       forced_image=options.image,
       use_cached=options.use_cached,
       port=options.port,
-      src_image=options.src_image)
+      src_image=options.src_image,
+      vm = options.vm)
 
   # Sanity-check for use of validate_factory_config.
   if not options.factory_config and options.validate_factory_config: