[VSphere] Improve performance of Fetching all VMs

``` ruby
#before
Benchmark.realtime{ Fog::Compute[:vsphere].servers(datacenter: 'supernap').all} # => 118.993048

#after (so far)
Benchmark.realtime{ Fog::Compute[:vsphere].servers(datacenter: 'supernap').all} # => 83.332368
```

Achieved by requesting all properties  for the entier VM view