* xenserver: attach regular iso with configdrive
Fixes#7902
This PR allows attaching a regular ISO to a VM when it already has the
config drive ISO attached.
Config-drive ISO is now attached with the SR name-label
<VM-NAME>-CONFIGDRIVE-ISO. While regular ISOs continue to attach with SR
name-label <VM-NAME>-ISO. VM which already have the configdrive ISO
attached before this fix will return an appropriate error and will need
to be stopped-start.