[Vsphere] Assign service to clone_result before new instance of vm

The previous code had the following error when cloning a vm on Vsphere:

```
~/fog-1.10.1/lib/fog/vsphere/models/compute/server.rb:122:in `clone': undefin
ed method `service=' for #<Fog::Compute::Vsphere::Server> (NoMethodError)
```

I fixed it by assigning the service before creating the new instance of "new_vm".

Can anyone review it? Thanks!