Fog::Compute.new().servers.create() returns wrong settings back

Currently if you create a server using
```ruby
compute = Fog::Compute.new(provider: :libvirt, libvirt_uri: 'qemu:///system')
result = compute.servers.create(cpu: { mode: 'host-passthrough' })
puts result
```
```
<Fog::Libvirt::Compute::Server
...
cpu={},
```

Then returned settings are defaults and not the ones that were set. This is not just for CPU but for other fields aswell.

