[docker] Fall back to tlcpackstaging in bash.sh

This uses apache#11775 to make local builds work if they're run in the meantime before CI tags over a new image to tlcpack

docker/bash.sh

@@ -290,7 +290,11 @@ DOCKER_DEVICES=( )
 # If the user gave a shortcut defined in the Jenkinsfile, use it.
 EXPANDED_SHORTCUT=$(lookup_image_spec "${DOCKER_IMAGE_NAME}")
 if [ -n "${EXPANDED_SHORTCUT}" ]; then
-    DOCKER_IMAGE_NAME="${EXPANDED_SHORTCUT}"
+    python tests/scripts/determine_docker_images.py "$DOCKER_IMAGE_NAME=$EXPANDED_SHORTCUT" 2> /dev/null
+    DOCKER_IMAGE_NAME=$(cat ".docker-image-names/$DOCKER_IMAGE_NAME")
+    if [[ "$DOCKER_IMAGE_NAME" == *"tlcpackstaging"* ]]; then
+        echo "WARNING: resolved docker image to fallback tag in tlcpackstaging" >&2
+    fi
 fi
 
 # Set up working directories