run_traffic: capture and exit gracefully if crash in trex run_traffic

run_traffic: capture and exit gracefully if crash in trex run_traffic

new non-blocking code of run_traffic has raise condition which causes
trex client to exit with STLError. This patches captures the exception
and exit gracefully

Traceback (most recent call last):
File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in
_bootstrap
self.run()
File "/usr/lib/python2.7/multiprocessing/process.py", line 114,
in run
self._target(*self._args, **self._kwargs)
File
"/opt/nsb_bin/yardstick_venv/lib/python2.7/site-packages/yardstick-0.1.dev0-py2.7.egg/yardstick/network_services/vnf_generic/vnf/sample_vnf.py",
line 945, in _traffic_runner
self.resource_helper.run_traffic(traffic_profile)
File
"/opt/nsb_bin/yardstick_venv/lib/python2.7/site-packages/yardstick-0.1.dev0-py2.7.egg/yardstick/network_services/vnf_generic/vnf/sample_vnf.py",
line 506, in run_traffic
self._run_traffic_once(traffic_profile)
File
"/opt/nsb_bin/yardstick_venv/lib/python2.7/site-packages/yardstick-0.1.dev0-py2.7.egg/yardstick/network_services/vnf_generic/vnf/tg_rfc2544_trex.py",
line 63, in _run_traffic_once
self.client.stop(self.my_ports)
File
"/opt/nsb_bin/trex/scripts/automation/trex_control_plane/stl/trex_stl_lib/trex_stl_client.py",
line 1202, in wrap2
raise STLError("'{0}' - connection to the server had been lost: '{1}'".format(func_name, client.conn.get_disconnection_cause()))
STLError:

Change-Id: Ie5741339451e0a3f9c4bb48f64fd35d86d18e5d4
Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>