Fsync data after writing prefs am: 49170aa3e3

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2320000

Change-Id: Ia7609e5929b1455ec227cc7415ce06c42a2496a5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>