add the ability to add hybrid ipv4/6 networks

[ramonskie]

currently google cpi only accepts 1 network interface
see https://github.com/cloudfoundry/bosh-google-cpi-release/blob/master/src/bosh-google-cpi/google/instance_service/networks.go#L30

added with commit de69e9c

a dualstack is availble in gcp docs see
https://cloud.google.com/compute/docs/ip-addresses/configure-ipv6-address#create-vm-ipv6

[ramonskie]

it seems that aws only support 1 network
https://github.com/cloudfoundry/bosh-aws-cpi-release/blob/master/src/bosh_aws_cpi/lib/cloud/aws/instance_param_mapper.rb#L95