Comment 2 for bug 1868100

Reviewed: https://review.opendev.org/713208
Committed: https://git.openstack.org/cgit/openstack/neutron-tempest-plugin/commit/?id=fd4141f2015d25f1b009d7cf2ebdd2907cd8e81a
Submitter: Zuul
Branch: master

commit fd4141f2015d25f1b009d7cf2ebdd2907cd8e81a
Author: Slawek Kaplonski <email address hidden>
Date: Sat Mar 14 14:34:00 2020 +0100

    Fix how nc is called in qos test

    We have already nc_listen method in base scenario tests class.
    It was since now used only in port_forwarding tests but we can
    reuse it in QoS tests also.

    There was also problem with spawning ncat process, that sometimes,
    without any clear reason for me, process wasn't spawned at all.
    That caused failure of test.

    So this patch adds new method ensure_nc_listen() which spawns ncat
    process on remote host and checkes if process is really spawned. That
    way we can avoid problems with not spawned ncat process.

    This patch also makes "server" attribute to be optional in nc_listen
    method. It is used only to log console output in case when ssh to the
    server wouldn't work as expected. And if server is not given,
    _log_console_output() method will list all servers which belongs to
    tenant and log console for each of them.

    Closes-Bug: #1868100

    Change-Id: I54c9f041f2f971219c32005b3fa573c06f0110ef