Merge "Clarification for PREPARE_UNATTENDED_REBOOT_ERROR" am: 11773facb7 am: 8e7f7303cf am: a3e52d2724

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1613109

Change-Id: I9fde6ebeeb2dd5ad38847317198cd05a8b29c0f1