network_ids is empty if network_id and network_name are not specified

Now network_ids is empty if network_id and network_name are not specified. This cause following error when 'vagrant up --provider=cloudstack' is executed.

.vagrant.d/gems/gems/fog-core-1.24.0/lib/fog/core/attributes.rb:147:in `requires': identity is required for this operation (ArgumentError)

When network_id and network_name are not specified in Vagrantfile, network_ids should be ommited.