Trivial update to handle new disk_info file and path permissions

In icehouse, Nova now creates a disk_info file in the instance
directory. This file's permissions need to be updated and the base
directory's permissions need to be chowned because that directory
maybe created ealier on in the process and the mkdir will not have
and effect.

Change-Id: Ia7412972fc14b58cf463ee827f28d7c4292027a4