Round partition sizes to multiple of 4K in delta_generator am: ab2e142328

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2528961

Change-Id: I078b72fef29fc1b05740568f988383305662b8f1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>