Bring install-time code inline with AOSP.

Recent submissions to AOSP rework some of the
internal logic of SELinuxMMAC and the PMS.
Bring our maintained version inline with
those changes while still allowing policy
to dictate all seinfo values regardless
of location.

Change-Id: I11ff4c4089217e6a9d95ca2841c5bc29bfd763ad
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>