Add shell commands to start checkpoint/check it is supported

Test: adb shell sm supports-checkpoint
Test: adb shell sm start-checkpoint 1 && adb reboot
Bug: 135984674
Change-Id: I08cd675b147cea88ad5b29ab4b0cd64ac445879d
Merged-In: I08cd675b147cea88ad5b29ab4b0cd64ac445879d
(cherry picked from commit 6d74942719bfedfe25f8c20af6fdd726ca14e15e)
2 files changed