Code review feedback & back-ground traffic support

Code review feedback & back-ground traffic support

Various code review comments taken into account. We also support now
background traffic, meaning the scripts will start a test between
machines and monitor packet loss, latency, etc., but at the same time,
the script will also start traffic on background machines. That traffic
will not be monitored. Each generator will generate the same ammoung of
traffic.

Change-Id: I5cd495be230a526f91de965f3d4dd0581681f5ca
Signed-off-by: Luc Provoost <luc.provoost@intel.com>