Maybe refactor worker + task code to use polymorphism

[feloxyde]

Is your refactor request related to a problem? Please describe. The current construction of Worker + Task code (especially worker.handleExecution method) is implemented as : Tasks have a "type", and Worker uses a "switch" to call the right method to use to run the task. This code could, maybe, be more elegant using interface and polymorphism, and thus allow easier implementation of new task types.

Describe the solution you'd like Define a "Task" interface, with a method like "run" or something like this, and have each task type implement it. Then the runner has to simply call "run" method instead of checking the type of the Task.

[loicalbertin]

We identified a major refactoring on tasks/workers for a future 4.0 release of Yorc. Keep in mind that we expect to not break dependencies across minor releases (see https://golang.org/doc/go1compat) so till 4.0 changes should be limited to package unexported stuff. Last warning the worker code is a bit touchy as it requires synchronization between Yorc instances especially when handling workflows steps that may be executed on several instances. This part of code is very sensitive and should be modified carefully (and well tested in live).

[feloxyde]

Oh right, I'll just leave this here waiting for the 4.0 release. I was expecting something like this to be, since workers are concurrent execution, thank you for removing "good first issue" label then !