Add Neutron benchmarks scenario for creating and listing ports

Scenario NeutronNetworks.create_and_list_ports is added, which does the following:
  - creates network
  - creates a given number of ports
  - lists ports

blueprint benchmark-scenarios-for-neutron

Change-Id: I029f220dd70beb0c248877bd4bd718dfa63aba40
Merge "Add Neutron benchmarks scenario for creating and listing ports"