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

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

Change-Id: I5fe67a74f175faa8133d3aef7c139c1b9e4f0fd3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>