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: Ie6fd49ad80ba6fa0e4e194a386549cac786b4bbe
Signed-off-by: Josh Stone <cuviper@gmail.com>