Also clarified the code in test_simpleperf.py.

Fixes #590

These include dropped pings and iperf hanging.

There are a bunch of these remaining, but I don't think the right course is
to 'fix' all of them to make pep8 happy, but instead to either change
the test in pep8 to consider that a continuation line may itself
be continued halfway, OR, to change the code in these lines to be more
readable by removing the need for all those nested continuations.

Personally, I find multiply-broken lines (aka nested continuations) really
hard to read.