When a VM is being migrated to a destination host it can be made
persistent on the destination by using '--persistent'. That may not
work as intended if '--xml' is used as well as that allows overriding
certain aspects of the VM xml, but does not involve the persistent
definition. In most cases users will need to supply also
'--persistent-xml' with the same set of modification.
Modify the man page to clarify the above so that users don't end up with
broken VM after migrating and restarting it.
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>