Add Cloud Networks capabilities

Allows for the addition of isolated Cloud Networks to
instances. By default, instances will have a public and
ServiceNet network available. ServiceNet can be removed
by passing :no_servicenet to the network configuration.

config.vm.provider :rackspace do |rs|
  rs.network '443aff42-be57-effb-ad30-c097c1e4503f'
  rs.network '5e738e11-def2-4a75-ad1e-05bbe3b49efe'
  rs.network :no_servicenet
end