android root: restore context for android system root

In this patchset we will store and reset the android system
root context after a wipe and restore to prevent issues
with no context labels in the file_contexts being applied.
This will prevent no boot issues in android with selinux
denials on the system root partition.

Change-Id: I87fd3a6060fbaa3e7bdfd7a4b1d09feeb4fa3f27
(cherry picked from commit 35d2bfda3c89ebd212a9bd2328bffd7464f95d47)
3 files changed