Move FinishedSnapshotWrites call back to PostinstallRunnerAction am: 19acf4fe19 am: 946276153d am: 4b19c13c52

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2901827

Change-Id: I52ea1634877306b65124214273441a07b158b383
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>