Merge "Protect userlist.xml and <user>.xml from corruption." into udc-dev am: 5c45e708

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22307542



Change-Id: Ic156f601212ce32c1461ce1028d432f8b9c81fae
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>