Fix libvirt evacuate instance on shared storage fails

When evacuate instance which has config drive enabled on shared storage,
disk.config file can't be created because of permision error, chowns
disk.config if it already exists.

Change-Id: I20bafc3482ead30297ad5402a09e97141816f4d1
Closes-Bug: 1247526
Merge "Fix libvirt evacuate instance on shared storage fails"