MountService: Remount all volumes after USB disconnect

If USB was removed while UMS was enabled, the MountService was only
remounting the primary share.  Any other shares, like the HTC Inc's
emmc, were left in limbo.  This patch now iterates over *all* shared
volumes to remount after disconnect.

Change-Id: Icf6c3d5396ea762aeb223869c380c5c3757d5652
Signed-off-by: Josh Stone <cuviper@gmail.com>