Add Network Subnet Support

[iainbrighton]

With the impending NAT configuration and to be able to support AWS and Azure (in the future) we will need to start attaching subnet information to the virtual switch definitions. This will be required to add NAT translation address and add routing information in AWS/Azure.

Something like this is what I think is needed:

@{
    AllNodes = @()
    NonNodeData = @{
        VirtualEngineLab = @{
            Network = @(
                @{ Name = 'Private'; Type = 'Internal'; Subnet = '192.168.10.0/24'; }
                @{ Name = 'Internet'; Type = 'NAT'; Subnet = '192.168.11.0/24'; }
            )
        }
    }
}

Unfortunately, I think we will have to make this mandatory for all network/switch defnitions?

[iainbrighton]

@janegilring This might have a bearing on thoughts about how we implement #126