Map all partitions before calling FinishUpdate for VAB as well am: b88b4ba12a

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3472588

Change-Id: I7e24019081e138cec44aaa016e9b7f0c2f795025
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>