Avoid self-overpping SOURCE_COPY ops by split them am: 58480ef4e5 am: ed66259209

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1518963

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I0c60c531d9bb30538c5acf846241abd48ce05b98