Settings: Add developer setting for root access

Also includes following change:

    Settings: Set root access options appropriately

    It is possible to be running a user build with a debuggable boot image.
    In this case, "su" will not be available.  So only show none/adb.

    Issue-Id: BACON-4461
    Change-Id: Iaa7df8311b9ea81eabb1566ba6f9159fdc9fab34

Change-Id: If96219d893c0dfdcf4ad36e1cd8de3a413db0e8b