Added support in openstack connector for additional disks, either empty or...

Added support in openstack connector for additional disks, either empty or based on an image. Warning! Tested only for v2 Openstack API. Changes for v3 were not implemented

Change-Id: Ice2b39d05620ca3eb90704c07d0c5919e4474793
Signed-off-by: montesmoreno <pablo.montesmoreno@telefonica.com>