[WIP] Iperf3 support

[teto]

To test, you have to use iperf3 from https://github.com/RichardWithnell/iperf/tree/dce or https://github.com/teto/iperf/tree/matt
and compile it with
./configure CFLAGS="-g -U_FORTIFY_SOURCE -fPIC" LDFLAGS="-pie -rdynamic" --with-pic --disable-shared --disable-static(otherwise it generates a shell script one can't use within dce).

For now test fails with error 'Unable to create a new stream'.

Related to #27

[teto]

I went back to this and found the culprit:
In iperf3, this failed because template = "/tmp/XXXXXX" and DCE does not create /tmp by default thus the call to mkstemp fails.

    /* Create and randomize the buffer */
    sp->buffer_fd = mkstemp(template);
    if (sp->buffer_fd == -1) {
        fprintf(stderr, "iperf: mkstemp\n");
        i_errno = IECREATESTREAM;
        free(sp->result);
        free(sp);
        return NULL;
    }

This is an issue that keeps hitting me in the back, I wish DCE could create some basic filesystem at the start, and simplify the way it handles path, wouldn't it be possible to use chroot everytime a node wakes up instead of regenerating filenames ?

Anyway, according to dce-iperf.cc,

  PointToPointHelper pointToPoint;
  pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));

but then iperf3 says that the sender sends more than 5Mbps (even though the receiver is ok), does it make sense ? are the extra packets rejected by the traffic control and reinjected later ?

    "end":  {
        "streams":  [{
                "sender":   {
                    "socket":   5,
                    "start":    0,
                    "end":  10.0001,
                    "seconds":  10.0001,
                    "bytes":    6320520,
                    "bits_per_second":  5.05637e+06,
                    "retransmits":  104,
                    "max_snd_cwnd": 146248,
                    "max_rtt":  241732,
                    "min_rtt":  125458,
                    "mean_rtt": 189064
                },
                "receiver": {
                    "socket":   5,
                    "start":    0,
                    "end":  10.0001,
                    "seconds":  10.0001,
                    "bytes":    6164136,
                    "bits_per_second":  4.93127e+06
                }
            }],
        "sum_sent": {
            "start":    0,
            "end":  10.0001,
            "seconds":  10.0001,
            "bytes":    6320520,
            "bits_per_second":  5.05637e+06,
            "retransmits":  104
        },
        "sum_received": {
            "start":    0,
            "end":  10.0001,
            "seconds":  10.0001,
            "bytes":    6164136,
            "bits_per_second":  4.93127e+06
        },
        "cpu_utilization_percent":  {
            "host_total":   0,
            "host_user":    13.4072,
            "host_system":  1.15032,
            "remote_total": 0,
            "remote_user":  10.1644,
            "remote_system":    0.815329
        }
    }
}