builder: update heartbeat timestamp on log message

buildman/component/buildcomponent.py

@@ -195,6 +195,9 @@ class BuildComponent(BaseComponent):
 
   def _on_log_message(self, phase, json_data):
     """ Tails log messages and updates the build status. """
+    # Update the heartbeat.
+    self._last_heartbeat = datetime.datetime.utcnow()
+
     # Parse any of the JSON data logged.
     docker_data = {}
     if json_data: