SCVMM - Gracefully handle hosts with no IP addresses

A user in the community ran into a situation where PowerShell reports no IP addresses for one of their hosts, causing the worker to bomb out. This PR gracefully handles this.
Style-wise, I think I prefer:

```ruby
return nil if nic[:Props][:IPAddresses].empty?
return nic[:Props][:IPAddresses][0][:MS][:IPAddressToString]
```

The way it's laid out now hides the `nil` in the middle of that statement.