xen: scsiback: add LUN of restored domain

When a xen domain is being restored the LUN state of a pvscsi device
is "Connected" and not "Initialising" as in case of attaching a new
pvscsi LUN.

This must be taken into account when adding a new pvscsi device for
a domain as otherwise the pvscsi LUN won't be connected to the
SCSI target associated with it.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>