Meaningful message for fail/success/pause transition

Implementation of this spec will allow workflow author to
define meaningful message for fail/success/pause transition.

Change-Id: Ie196763a4a340b8cd92cf552a8a8b4acbc05d0bd
Implements: blueprint mistral-fail-transition-message

AUTHORS

@@ -1,2 +1,3 @@
 Lingxian Kong <anlin.kong@gmail.com>
 Winson Chan <wcchan@stackstorm.com>
+hparekh <hardik.parekh@nectechnologies.in>

specs/mitaka/approved/mistral-fail-transition-message.rst

@@ -0,0 +1,105 @@
+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+================================
+Customize message for Transition
+================================
+
+https://blueprints.launchpad.net/mistral/+spec/mistral-fail-transition-message
+
+
+Problem description
+===================
+
+Currently, "fail" command fails the workflow and the user needs to check the
+different entities and flow to find why workflow has been failed. So, the
+workflow execution is failed but there is no meaningful error message.
+
+Use Cases
+---------
+
+As a user, I want to provide customized message for fail/success/pause
+transition in 'on-success', 'on-complete' and 'on-error'.
+
+
+Proposed change
+===============
+
+To solve this problem, I would like to add 'msg' input argument for
+fail/success/pause commands. This argument will be publish to the
+context before running fail/success/pause. Please consider following
+example::
+
+    ...
+    tasks:
+      t1:
+        action: ...
+        on-success:
+          - fail(msg='var1 is null.'): <% $.var1 = null %>
+          - succeed(msg='var1 is not null.')
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+End user impact
+---------------
+
+User can pass 'msg' argument for fail/success/pause commands. This argument
+will be optional.
+
+Performance Impact
+------------------
+
+None
+
+Deployer impact
+---------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+hardik <hardik.parekh@nectechnologies.in>
+
+Work Items
+----------
+
+* Add input argument 'msg' for fail/success/pause commands.
+
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+Tests should cover all the scenarios mentioned in use cases section.
+
+
+References
+==========
+
+https://review.openstack.org/#/c/276625/