devserver support for update images from buildbot.

Remove implicit sudo from gpt partition packing scripts.

Misc cleanup and fixes included.

Review URL: http://codereview.chromium.org/1633018
diff --git a/autoupdate.py b/autoupdate.py
index ac66d51..47e6211 100644
--- a/autoupdate.py
+++ b/autoupdate.py
@@ -98,8 +98,12 @@
     else:
       image_file = 'chromiumos_image.bin'
     if self.serve_only:
-      os.system('cd %s && unzip -o image.zip' %
+      err = os.system('cd %s && unzip -o image.zip %s unpack_partitions.sh' %
                 (image_path, image_file))
+      if err:
+        web.debug('unzip image.zip failed.')
+        return False
+
     os.system('rm -f %s/part_*' % image_path)
     os.system('cd %s && ./unpack_partitions.sh %s' % (image_path, image_file))
     shutil.move(os.path.join(image_path, 'part_2'), kernel_file)