am aa6dbe21: Try to fix system.img in update zip file.

Merge commit 'aa6dbe2144196bb6f9c1b6b539126250f9ef8af6' into gingerbread-plus-aosp

* commit 'aa6dbe2144196bb6f9c1b6b539126250f9ef8af6':
  Try to fix system.img in update zip file.