add network device

Add new resource network device like router, switch
maas has fabrc devie and network function:
https://maas.ubuntu.com/docs/networking.html
Neutron with Ironic already cover the network function,
the network device here is mostly to show physic connection,
so nimble better the ability to render connection graphic like Vitrage project.

Vitrage project is the OpenStack RCA (Root Cause Analysis) service for organizing, analyzing and expanding OpenStack alarms & events, yielding insights regarding the root cause of problems and deducing their existence before they are directly detected.
https://wiki.openstack.org/wiki/Vitrage
Vitrage uses vm/physic switch connection map to do route cause analysis.