message: data_str field in python3 is bytes.  Decode to string using decode()
  Summary:
  As with other places which decode a string field in a protobuf, need
  to have decode() to turn bytes into an actual string
  Test Plan: Local testing only
  Reviewers: georgep
diff: @@ -91,17 +91,18 @@ def extract_all_strings_from_event_trace(events):
  evt_str = "Compile begin: " + evt.module_name + "\n"
  elif evt.type == IpuTraceEvent.COMPILE_END:
  evt_str = "Compile end: " + evt.module_name + "\n" + \
  - "Duration: " + str(evt.data_int) + " us\n" + evt.data_str
  + "Duration: " + str(evt.data_int) + " us\n" + \
  + evt.data_str.decode('utf-8')
  elif evt.type == IpuTraceEvent.HOST_TO_DEVICE_TRANSFER:
  - evt_str = "Host->Device\nHandle = " + evt.data_str + "\n"
  + evt_str = "Host->Device\nHandle = " + evt.data_str.decode('utf-8') + "\n"
  #"Bytes = " + str(evt.data_int)
  elif evt.type == IpuTraceEvent.DEVICE_TO_HOST_TRANSFER:
  - evt_str = "Device->Host\nHandle = " + evt.data_str + "\n"
  + evt_str = "Device->Host\nHandle = " + evt.data_str.decode('utf-8') + "\n"
  #"Bytes = " + str(evt.data_int)
  elif evt.type == IpuTraceEvent.LOAD_ENGINE:
  evt_str = "Load engine: " + evt.module_name + "\n"
  elif evt.type == IpuTraceEvent.EXECUTE:
  - evt_str = "Execute\n" + evt.data_str
  + evt_str = "Execute\n" + evt.data_str.decode('utf-8')
  else:
  evt_str = "Unknown event"
  