Instead of having smart workers that need to know
about the full logic of how they operate and what
they will do which makes it hard to reuse parts of
those workers switch the model so that workers are
dumb and they just run tasks which themselves can
request additional tasks to run when succesful.

This makes it more consistent when tasks are to
be retried and also makes it easier to know which
task is running and when.

Less specialized workers == good.

Closes-Bug: #1586474

Change-Id: Ie7b7303b8bf2a80b3e26b6d4ffc27787f8c794d6