netdetect: Computing maths on streams

As every hosts will run several clients, it's important to compute
mathematical results to estimate how good was the run.

For each host the following performance results will be shown:

- How many MBits per sec this host generated (bw_host)
- How many clients (or remote hosts) were running (streams_count)
- What performance for the slower stream ? (bw_stream_min)
- What performance for the fastest stream ? (bw_stream_max)
- What is the average performance for the streams ? (bw_stream_average)
- What is the median performance for the streams ? (bw_stream_median)
- What is the standard deviance between streams ? (bw_stream_dev)
- What were the raw values for all streams ? (bw_stream_raw_values)

bw_stream_raw_values will be useful to compute results at the cluster's scale instead of at a host level.

Here come a typical output:
 ('network', 'tcp_bench', 'bw_host', '852.8'),
 ('network', 'tcp_bench', 'streams_count', '2'),
 ('network', 'tcp_bench', 'bw_stream_min', '402.42'),
 ('network', 'tcp_bench', 'bw_stream_max', '450.38'),
 ('network', 'tcp_bench', 'bw_stream_average', '426.4'),
 ('network', 'tcp_bench', 'bw_stream_median', '426.4'),
 ('network', 'tcp_bench', 'bw_stream_stddev', '23.98'),
 ('network', 'tcp_bench', 'bw_stream_raw_values', '[402.42, 450.38]')
netdetect: Remove useless semicolon
netdetect: Don't print on stdout

Using stdout is a very bad idea as stdout is put with the structure.
It should have been on stderr instead.