Properly support neutron subnet `host_routes` on the router appliance.
Refactor the `host_routes` logic a bit.
Make `_alter_route` return an explicit boolean to indicate success or failure.
Add a test for `route` call failures.
Merge pull request #50 from ryanpetrello/feature-support-host-routes

Properly support neutron subnet `host_routes` on the router appliance.