Mistral/Blueprints/repeater

As per various discussion on changed the specification.

The DSL snippet:

       repeat_task:
           action: action_name
           repeat:
               iterations : iterations
               delay : delay_in_sec
               break-on : yaql_expr
           on-finish:
               on_finish_task_ref : yaql_expr
           on-error:
               on_error_task_ref

1. This is a mechanism to repeat a specific action as per the repeat specification. 2. 'repeat' is an optional property of the Task. 3. on-finish/on-error/on-success i.e. and subsequent tasks are only scheduled after iterations are complete.

The original design and parts of that discussion will be used to implement a mechanism to repeat a set of tasks. However, this will require calling out to other workflows and requires a separate blueprint. (TODO add link.)

Etherpad https://etherpad.openstack.org/p/std_repeat