upgrade: allow to add host to updated cluster

Fix "Answer file lacks lockspace UUIDs, please use an answer file
generated from the same version you are using on this additional host"
Error while adding a host 3.5 based to a NFS cluster upgraded from 3.4.

Change-Id: Id77da1857d379910b41764133eb5c0b82c5a3054
Bug-Url: https://bugzilla.redhat.com/1163385
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>