Configure network port number

Port 0 is currently hardcoded. The guest image tools will always configure port 0. [2]

Neutron provides the following information to nova-dpm
* vif-type (only 'dpm_vswitch' implemented as of now)
* object_id

Nova-dpm needs to do the following (pseudo code)

if vif_type == 'dpm_vswitch':
  port = retrieve_port_no_from_vswitch_obj(object_id = object_id)
  [1]
else
  # We never should have gotten so far, as another type is not supported

[2] https://github.com/openstack/nova-dpm/blob/bc6a8828b6f49dd8b5b38da2fff8a62d66a6c0fa/nova_dpm/virt/dpm/driver.py#L305,307