Create a per-boot key on each boot

Bug: 140882488
Test: Booted twice, checked logs to ensure encryption
    is different each time, adb created files in directory.
Cherry-Picked-From: c8a3ef3f3c501c7bc14a2078dde513765cdb56d7
Merged-In: I74077bf8f727dab726c25f512ed7406a74cbe0bf
Change-Id: I74077bf8f727dab726c25f512ed7406a74cbe0bf
3 files changed