Make action responses declarative

We have 2 issues with the current action system:

• You can't return an object, you must return a dict or a list of dicts otherwise the action runner doesn't deserialise the response correctly. So every action pack has it's own way of acheiving the same thing- mapping iteritems on an instance to a dictionary.
• When writing workflows in Mistral, there is no typeahead or checking for field names in variables, same goes for jinja templates in aliases and rules

What I would really like to see is something like this in .yaml

---
name: balancer_attach_member
runner_type: python-script
description: Attach a member to a load balancer
enabled: true
entry_point: balancer_attach_member.py
parameters:
  region:
    type: string
    description: The region code
    default: dd-na  
schema:
  type: instance|list|dynamic
  fields:
    id:
      type: integer
    name:
      type: string

Then, the Run method of a BaseAction has a wrapper function which performs a dictionary map based on the schema.

The knock on effects are:

• Mistral can be statically validated
• Jinja templates in rules and aliases can be statically validated instead of the trial and error testing that currently exists
• You can see what the response of an action looks like without having to execute it first, making developing workflows a lot faster
• You don't need to write a mapper function for every action

I appreciate this is very "unpythonic" so the schema type would be dynamic by default for people that don't want to be tied down.

Start by tracing the action runner and the BaseAction Run method, then review the proposed action YAML schema and its references to Mistral, Jinja templates, rules, and aliases. Done would mean declarative response schemas support instance, list, and dynamic types, enable validation and response inspection, and retain dynamic behavior by default.