Improve IXIA IxNetwork library and traffic profile (4)

Improve IXIA IxNetwork library and traffic profile (4)

This patch implements an active wait for the traffic injection. Once the
traffic is started, the traffic generator class will poll periodically the
IXIA traffic generator chassis to retrieve the status of the traffic
("started", "stopped").

Now the latency statistics are retrieved and reported for each injection
period.

JIRA: YARDSTICK-1116

Change-Id: I4422e2c88b4fc97b7cac3de8a82b2d75467c4117
Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>
Signed-off-by: Emma Foley <emma.l.foley@intel.com>