Reserve space for apex by creating a file and write 0s am: 8933d5721a am: d2fcb43bb8

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1563752

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I510405861786cc65f90a5a3e0d2d14c3c29f52e8