CH-185 On-exit strategy add custom image parameter

Author: filippomc

docs/applications/development/workflows-api.md

@@ -247,6 +247,18 @@ op = operations.ParallelOperation(..., on_exit_notify=on_exit_notify)
 
 Synchronous operation types use this mechanism to wait for the result and get the value.
 
+To customize the onExit strategy an additional `image` parameter can be specified. 
+
+```Python
+import json
+on_exit_notify={
+    'queue': 'my_queue',
+    'payload': json.dumps({'insert': 1})
+    'image': "my-image"
+}
+op = operations.ParallelOperation(..., on_exit_notify=on_exit_notify)
+```
+
 ## Free template customization
 
 To customize the task beyond the Task api, use 

libraries/cloudharness-common/cloudharness/workflows/operations.py

@@ -168,7 +168,7 @@ def add_on_exit_notify_handler(self, spec):
         payload = self.on_exit_notify['payload']
         exit_task = CustomTask(
             name="exit-handler",
-            image_name='workflows-notify-queue',
+            image_name=self.on_exit_notify('image', 'workflows-notify-queue'),
             workflow_result='{{workflow.status}}',
             queue_name=queue,
             payload=payload