Manual coalesce for a VM

[olivierlambert]

See https://docs.xenserver.com/en-us/xenserver/8/storage/manage.html#reclaim-space-by-using-the-offline-coalesce-tool

In Advanced view, a "Manual coalesce" button that will show a popup "The VM will be suspended during the operation".

Then:

1. Suspend the VM
2. Start the command
3. Unsuspend when finished