Add new API for unattended reboot.

CTS-Coverage-Bug: 179310594
Bug: 160784387
Test: manual
Change-Id: I59b7ff7afec9846a114ee8d20f14d22cf69f0680
Merged-In: I59b7ff7afec9846a114ee8d20f14d22cf69f0680
(cherry picked from commit 726fa0a5f400f95558dcb31effbb98fee67b54ed)
6 files changed