Add an API in update_engine to switch the slot back and forth am: da607a35bd am: c359236ab2 am: cc2fd47f4e am: 4ce1bcc700 Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1697663 Change-Id: I8ff6f6c82c899bb96213761005f1c226850279db GitOrigin-RevId: b0bf0e3753c7a261670b0066dd6b403655d1e5f6