The iperf version used in older version of CI docker images had the
following output format:
[ 3] 0.0-10.0 sec 1.25 MBytes 1.05 Mbits/sec 0.000 ms 0/ 892 (0%)
The newer iperf version which was recently included in the container
prints more digits after the decimal point:
[ 3] 0.0000-10.0148 sec 1.25 MBytes 1.05 Mbits/sec 0.002 ms 0/ 895 (0%)
The regular expression to match this line expected a single zero after
the decimal point, so the new format no longer matches.
The fix is to expect any number of digits in the fractional part.
1. fix TypeError when running with python3
2. fix throughput chart x/y axis label error
3. make test case compatibile with iperf bin on earlier release branches
