simulate_ota.py: truncate partitions to multiples of 4 KiB am: a2e0fe38b4 am: aa1653f1ee

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2083404

Change-Id: I433993cab266925d1650de0a41b62d6db2dde599
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>