agent: Add explicit start to BatchingTelemetryMessenger

My original plan was to start a thread in __init__() and stop the thread
when __del__() was called. Since the running thread (object) contains a
reference to the BatchingTelemetryMessenger object that launched it, the
destructor will not be called until the thread is stopped. Therefore, a
stop() was added to allow the BatchingTelemetryMessenger to be stopped.
Since it has an explicit stop, it should also have an explicit start,
rather than starting the thread in the constructor.

monkey/infection_monkey/monkey.py

@@ -474,6 +474,7 @@ class InfectionMonkey(object):
     def run_ransomware():
         telemetry_messenger = LegacyTelemetryMessengerAdapter()
         batching_telemetry_messenger = BatchingTelemetryMessenger(telemetry_messenger)
+        batching_telemetry_messenger.start()
         try:
             RansomewarePayload(
                 WormConfiguration.ransomware, batching_telemetry_messenger

monkey/infection_monkey/telemetry/messengers/batching_telemetry_messenger.py

@@ -28,14 +28,16 @@ class BatchingTelemetryMessenger(ITelemetryMessenger):
         self._last_sent_time = time.time()
         self._telemetry_batches: Dict[str, IBatchableTelem] = {}
 
+    def __del__(self):
+        self.stop()
+
+    def start(self):
+        self._should_run_batch_thread = True
         self._manage_telemetry_batches_thread = threading.Thread(
             target=self._manage_telemetry_batches
         )
         self._manage_telemetry_batches_thread.start()
 
-    def __del__(self):
-        self.stop()
-
     def stop(self):
         self._should_run_batch_thread = False
         self._manage_telemetry_batches_thread.join()

monkey/tests/unit_tests/infection_monkey/telemetry/messengers/test_batching_telemetry_messenger.py

@@ -57,6 +57,7 @@ class BatchableTelemStub(BatchableTelemMixin, BaseTelem, IBatchableTelem):
 def batching_telemetry_messenger(monkeypatch, telemetry_messenger_spy):
     patch_time(monkeypatch, 0)
     btm = BatchingTelemetryMessenger(telemetry_messenger_spy, period=0.001)
+    btm.start()
     yield btm
 
     btm.stop()