Decoupled callback functions from BaseTask Class

--- Removed all callback functions from 'jobs.py' and put them in a new file '/awx/main/tasks/callback.py'
--- Modified Unit tests unit moved
--- Moved 'update_model' from jobs.py to /awx/main/utils/update_model.py

awx/main/utils/update_model.py

@@ -0,0 +1,40 @@
+from django.db import transaction, DatabaseError
+
+import logging
+import time
+
+
+logger = logging.getLogger('awx.main.tasks.utils')
+
+
+def update_model(model, pk, _attempt=0, **updates):
+    """Reload the model instance from the database and update the
+    given fields.
+    """
+    try:
+        with transaction.atomic():
+            # Retrieve the model instance.
+            instance = model.objects.get(pk=pk)
+
+            # Update the appropriate fields and save the model
+            # instance, then return the new instance.
+            if updates:
+                update_fields = ['modified']
+                for field, value in updates.items():
+                    setattr(instance, field, value)
+                    update_fields.append(field)
+                    if field == 'status':
+                        update_fields.append('failed')
+                instance.save(update_fields=update_fields)
+            return instance
+    except DatabaseError as e:
+        # Log out the error to the debug logger.
+        logger.debug('Database error updating %s, retrying in 5 seconds (retry #%d): %s', model._meta.object_name, _attempt + 1, e)
+
+        # Attempt to retry the update, assuming we haven't already
+        # tried too many times.
+        if _attempt < 5:
+            time.sleep(5)
+            return update_model(model, pk, _attempt=_attempt + 1, **updates)
+        else:
+            logger.error('Failed to update %s after %d retries.', model._meta.object_name, _attempt)