Add NSM gw-routers example to CNF Testbed

[michaelspedersen]

Goal: Add NSM gw-rotuers example to CNF Testbed as discussed on weekly meetings.

              +---------+              +--------+              +--------+              +---------+
 10.60.0.0/24 |         | 10.60.1.0/24 |        | 10.60.2.0/24 |        | 10.60.3.0/24 |         | 10.60.4.0/24
--------------+ Gateway +--------------> Router +--------------> Router +--------------> Gateway +--------------
              |    L    |              |   L    |              |   R    |              |    R    |
              +---------+              +--------+              +--------+              +---------+

Tasks:

• [x] Create yaml description file(s) for example
  • External endpoints (gateways) will likely need a some modification to run on CNF Testbed deployment
  • Still relies on running privileged for NIC interfaces (using vfio-pci driver)
• [x] Test connectivity using ping
• [x] Add documentation