Add admin utilities to list and clean backend logical routers that does
not exist in neutron.
Usage:
nsxadmin -r orphaned-routers -o list
nsxadmin -r orphaned-routers -o nsx-clean --property nsx-id=<id>
Change-Id: I69dcb2abcf798c3c35f7ddde1c8a10a16a44cc3e
1b6d00ac66