Prior to Grizzly release default instance directory names were based on
instance.id field, for example directory for instance could be named
``instance-00000008``. In Grizzly this mechanism was changed,
instance.uuid is used as an instance directory name, e.g. path to instance:
In Newton backward compatibility is dropped. For instances that haven't
been restarted since Folsom and earlier maintanance should be scheduled
before upgrade(stop, rename directory to instance.uuid, then start) so Nova
will start using new paths for instances.