Enable the MQ producer in "SampleVNFTrafficGen" class

Enable the MQ producer in "SampleVNFTrafficGen" class

Now all traffic generators using the default implementation of
"ClientResourceHelper.run_traffic" will update the status of
the traffic injection using the MQ.

The available methods are listed in common.messsaging (VNF_METHOD_*):
- tg_method_started: VNF app started
- tg_method_finished: VNF app finished
- tg_method_iteration: VNF app execution loop started

JIRA: YARDSTICK-1127

Change-Id: I12829e1762fc20cc95da3b50767a66f031e25ee8
Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>