Changing series to vivid

Change-Id: Ic59d729c0b851e72e854718b8861d66ee5d5506a
Signed-off-by: Ricardo Salveti de Araujo <rsalveti@rsalveti.net>
update-system-img.sh: make sure /data is mounted first

We're not automatically mounting /data anymore, so in order to replace
the android system image, we first need to make sure that /data is
available.

Change-Id: I33402a2eecfe19f10e806fc484cfa967ff727693
Signed-off-by: Ricardo Salveti de Araujo <rsalveti@rsalveti.net>