Fix RemovedInDjango19Warning warnings

TNL-3450

.travis.yml

@@ -37,5 +37,7 @@ script:
 branches:
     only:
       - master
+      - ora-staff-grading
+      - ned/django-upgrade-1.8
 after_success:
   coveralls

openassessment/assessment/models/ai.py

@@ -5,8 +5,9 @@ from uuid import uuid4
 import json
 import logging
 from django.conf import settings
+from django.core import signals
 from django.core.files.base import ContentFile
-from django.core.cache import cache, get_cache
+from django.core.cache import cache, _create_cache
 from django.db import models, transaction, DatabaseError
 from django.utils.timezone import now
 from django_extensions.db.fields import UUIDField
@@ -21,11 +22,23 @@ AI_ASSESSMENT_TYPE = "AI"
 logger = logging.getLogger(__name__)
 
 
+def create_cache(backend, **kwargs):
+    """
+    Create cache backend. Using this custom function to avoid deprecation warnings.
+    """
+    cache = _create_cache(backend, **kwargs)
+    # Some caches -- python-memcached in particular -- need to do a cleanup at the
+    # end of a request cycle. If not implemented in a particular backend
+    # cache.close is a no-op
+    signals.request_finished.connect(cache.close)
+    return cache
+
+
 # Use an in-memory cache to hold classifier data, but allow settings to override this.
 # The classifier data will generally be larger than memcached's default max size
 CLASSIFIERS_CACHE_IN_MEM = getattr(
     settings, 'ORA2_CLASSIFIERS_CACHE_IN_MEM',
-    get_cache(
+    create_cache(
         'django.core.cache.backends.locmem.LocMemCache',
         LOCATION='openassessment.ai.classifiers_dict'
     )
@@ -33,7 +46,7 @@ CLASSIFIERS_CACHE_IN_MEM = getattr(
 
 CLASSIFIERS_CACHE_IN_FILE = getattr(
     settings, 'ORA2_CLASSIFIERS_CACHE_IN_FILE',
-    get_cache(
+    create_cache(
         'django.core.cache.backends.filebased.FileBasedCache',
         LOCATION='/tmp/ora2_classifier_cache'
     )

openassessment/fileupload/backends/filesystem.py

@@ -61,7 +61,7 @@ def get_cache():
     cache_name = getattr(settings, "ORA2_FILEUPLOAD_CACHE_NAME", None)
     if cache_name is None:
         raise exceptions.FileUploadInternalError("Undefined cache backend for file upload")
-    return django.core.cache.get_cache(cache_name)
+    return django.core.cache.caches[cache_name]
 
 
 def make_upload_url_available(url_key_name, timeout):