test_iperf3() is a pretty inscrutable mess of nested background processes.
It has a number of ugly sleeps needed to wait for things to complete.
Rewrite it to be cleaner:
* Use the construct (a & b & wait) to run 'a' and 'b' in parallel, but
then wait for them both to complete before continuing
* This allows us to wait for both the server and client to finish, rather
than sleeping
* Use jq to do all the math we need to get the final result, rather than
jq followed by some complicated 'bc' mangling
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
e5e10aff81