Fix mounting of ext4 formated sdcards

FileUtils.getVolumeUUID(path) doesn't return a uuid for ext4 formated
sdcards.

Using actualVolume.getUuid()and parsing the returned value works for all
file systems.

Change-Id: I77fe9e09b523bcba68dd2409def68acb715ca33c
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>