Routing test cases

@thaller mentioned that we should ensure that these scenarios work, maybe they are already tested, if not, please add tests.

Given a host without a direct route to 203.0.113.1, when I add a route like ipv4.routes "198.51.100.0/24 203.0.113.1" to a profile for device net0 with NM, then the profile will activate successfully and ip route list will show the route like "198.51.100.0/24 via 203.0.113.1" and ip route will show "203.0.113.1 dev net0".

Given a host without a direct route to 203.0.113.1, when I add a route like ipv4.routes "0.0.0.0/0 203.0.113.1" to a profile for device net0 with NM, then the profile will activate successfully and ip route list will show the route like "default via 203.0.113.1" and ip route show will show a direct route like "203.0.113.1 dev net0".

Ideally, similar tests for IPv6 should be created.

@ffmancera this might have been broken by NetworkManager!1025 (closed) ([thaller] correction: NetworkManager!1022 (closed)).