vold: mount ext4 with forced SELinux context

Always mount voldmanaged ext4 partitions with the SELinux sdcard_external
context. For other file systems, this is done via the genfs_context,
but since ext4 supports SELinux natively, it must be set here.

Change-Id: I1364f37018b25d79b1826c85849def64e868d72f
vold: allow non-vfat devices to be used as ASEC

CM supports alternative file systems (which some devices specify
in the fstab as 'auto').

Change-Id: I7e78fe87a7efc49d6749d5892107085d55156cce
vold: support more than 1 UMS share

Used for devices with both mountable internal and external sdcards.

This is a forward-port and clean up of the 10.2 code (which contains
a lot of deadcode.)

Original authors:

    Alex Zepeda <alex@inferiorhumanorgans.com>
    Genokolar <genokolar@gmail.com>
    Josh Stone <cuviper@gmail.com>
    mik_os <kiril.mik.os@gmail.com>
    Oran Avraham <oranav@gmail.com>
    Pawit Pornkitprasan <p.pawit@gmail.com>
    Tony Layher <layhertony@gmail.com>

Change-Id: I926ce244255414697373d26d252a9da89aea7226

Conflicts:
	VolumeManager.cpp

Conflicts:
	Android.mk
vold: Initialize flag variables

* These variables may actually be checked before they are set. Set them
  to reasonable defaults to prevent very strange behavior.

Change-Id: I303c4c6742ce86bbde6bda768f4e396263518ed2