update shell; add logging for image pulling before starting container

Author: dcloud347

argus/tools/shell.py

@@ -65,6 +65,8 @@ def _ensure_shell(self) -> pexpect.spawn:
 
         # Start container if needed
         if self._container is None:
+            logger.info("Pulling image %s (may take a while)", self.image)
+            self._client.images.pull(self.image)
             logger.info("Starting container from image %s", self.image)
             self._container = self._client.containers.run(
                 self.image,