trex: Add support for traffic capture

trex: Add support for traffic capture

A support of traffic capture was added into T-Rex.
It allows to write a functional tests, which will
verify proper vSwitch functionality by inspection
of packets received by T-Rex.
A testcase example was added into integration
testcases.

JIRA: VSPERF-556

Change-Id: I5ad28479ca2ec29760b68f24510af1a6d74866ae
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: Sridhar Rao <sridhar.rao@spirent.com>
Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>
Reviewed-by: Richard Elias <richardx.elias@intel.com>