--route option is used to set routes to the router.
It is used like this:
--route destination=subnet,gateway=ip-address
destination: destination subnet CIDR
gateway: nexthop IP address
--clear-routes is used to clear all routes on the router.
Change-Id: I97ce4871113c684b29c98cdad4dec9cc80ed20f7
Implements: blueprint neutron-client
Partial-bug: #1519503