Fix potential data-loss bug in disk wipe routines

For the 2.4 release, we only add the missing RPC calls. However, this
needs to be fixed properly, by preventing usage of mis-configured
disks.

Also add a bit more logging so that it's directly clear on which node
the wipe is being done.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>