Fix creation of EBS volumes for RAID

Without this patch the EBS volume is never created and so Chef gets
stuck, eg:

    [2013-10-10T13:44:30+00:00] INFO: Waiting for individual disks of RAID /data
    [2013-10-10T13:44:30+00:00] INFO: device /dev/xvdb not ready - waiting
    [2013-10-10T13:44:40+00:00] INFO: device /dev/xvdb not ready - waiting
    ...