[1.7.x] Fixed #22299 -- Cleanup wizard temp files when possible.

Thanks to @erikr for the review.

Backport of fa8b4735 from master.

django/contrib/formtools/tests/wizard/storage.py

 from datetime import datetime
 from importlib import import_module
+import os
+import tempfile
 
 from django.http import HttpRequest
 from django.conf import settings
-
 from django.contrib.auth.models import User
+from django.core.files.storage import FileSystemStorage
+from django.core.files.uploadedfile import SimpleUploadedFile
+
+
+temp_storage_location = tempfile.mkdtemp(dir=os.environ.get('DJANGO_TEST_TEMP_DIR'))
+temp_storage = FileSystemStorage(location=temp_storage_location)
 
 
 def get_request():

django/contrib/formtools/wizard/storage/base.py

@@ -27,6 +27,11 @@ class BaseStorage(object):
         }
 
     def reset(self):
+        # Delete temporary files before breaking reference to them.
+        wizard_files = self.data[self.step_files_key]
+        for step_files in six.itervalues(wizard_files):
+            for step_file in six.itervalues(step_files):
+                self.file_storage.delete(step_file['tmp_name'])
         self.init_data()
 
     def _get_current_step(self):

docs/ref/contrib/formtools/form-wizard.txt

@@ -634,9 +634,9 @@ storage class <builtin-fs-storage>`)::
 
 .. warning::
 
-    Please remember to take care of removing old files as the
-    :class:`WizardView` won't remove any files, whether the wizard gets
-    finished correctly or not.
+    Please remember to take care of removing old temporary files, as the
+    :class:`WizardView` will only remove these files if the wizard finishes
+    correctly.
 
 Conditionally view/skip specific steps
 ======================================