* The reason behing this renaming is that task being an action/workflow
invocation doesn't have input, it configures input for action/workflow.
So to distinguish this difference and simplify communication around
tasks it's been decided to rename 'task output' to 'task result'.
* Fixed required unit tests
* Removed weird transformation from 'output' to 'result' in task DB model
* Removed 'output' field in task REST resource, left only 'result'
(it caused a lot of confusion before)
* Created a stub for data flow evaluate_effective_task_result() method
that is supposed to calculate a final task result based on task
invocations
Change-Id: I8c0e159c5c074185e0edc1982a01ad4f525b4d11