Reland: Map all partitions before calling FinishUpdate for VAB as well am: 67b4378f2f

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3487611

Change-Id: Icf3106ef128466c3f1d796a433c75793be4464b8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>