docs: Dummy pre-configured results

docs: Dummy pre-configured results

In case of Dummy traffic generator, the test results
can be pre-configured. Configuration and examples
were described in trafficgen related chapter.

JIRA: VSPERF-458

Change-Id: I6179e98f3999e5b2df2ad4080582302bf4177cda
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Bill Michalowski <bmichalo@redhat.com>
Reviewed-by: Antonio Fischetti <antonio.fischetti@intel.com>
Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>