Add boot_status_prop for boot completed props

Assigning a new context boot_status_prop for following two properties:
- sys.boot_completed
- dev.bootcomplete

Bug: 154885206
Test: boot cf_x86 and crosshatch, see no denials
Change-Id: Ieadabf90a9a1b54b52a1283bd648c11c95d558dd
Merged-In: Ieadabf90a9a1b54b52a1283bd648c11c95d558dd
(cherry picked from commit 2973c9605555c119243ef85119576b2d01a12060)
8 files changed