This way we benefit from:
* knowing which attributes are used/required by each object class and
subclass
* Having validation function definitions near the class going to use them
Change-Id: I8fd6773c51d19405a585977af4ed72cad2b21db1
Some older iperf3 versions don't support the --logfile arg. Let's
instead parse the json from stdout. Old --logfile behavior is left in
code but disabled since it's a nicer (less hacky) way to get results,
because parsing from stdout means we need to avoid reading some content.
Change-Id: Ia1b7fa4dae074089878963aeddf0006aea68e31f