Minimal fix for adb backup.

In master this code has been completely rewritten. This is the minimal fix
against the mnc-sdk-release source.

Bug: http://b/23015233
Bug: https://code.google.com/p/android/issues/detail?id=183490
Change-Id: Iac30993bd2b1b354f8518d8ea2a9ae680ebe4177