Otter Grade Notebook Timeout Handled

- if notebook times out GradingResult object created that indicates catastrophic failure
- Failed notebook grading still results in final_grades.csv

otter/grade/containers.py

@@ -7,6 +7,7 @@
 import shutil
 import tempfile
 import zipfile
+from otter.test_files import GradingResults
 
 from concurrent.futures import ThreadPoolExecutor, wait
 from python_on_whales import docker
@@ -23,6 +24,10 @@
 LOGGER = loggers.get_logger(__name__)
 
 
+class TimeoutException(Exception):
+    pass
+
+
 def build_image(ag_zip_path: str, base_image: str, tag: str, config: AutograderConfig):
     """
     Creates a grading image based on the autograder zip file and attaches a tag.