Halve test erofs image size^2 am: bc185040f3

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2236834

Change-Id: I9179f83404e834d96ec64c8178b12ddb041c51e1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>