Topotests need to run on platforms besides linux

[donaldsharp]

Any changes to the southbound interface are very hard to test across all supported platforms. It would be super useful to have topotests be able to run across all platforms we currently support.

Work is being done to revamp the southbound interface and changes made are fragile on systems beyond linux because there is no good way to look changes on all systems

[mwinter-osr]

Getting it to work on ALL supported systems would probably be impossible unless we replace mininet. Mininet itself is in the process of getting ported to FreeBSD, so this might be possible. See https://wiki.freebsd.org/Mininet

Any takers to try it on mininet?