Support incremental OTA in ota_extractor am: 91e839cf19

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2056749

Change-Id: I71ab8b261458d2106c8b3df89d85bbd9b5933898
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>