Working on "join": fixing "partial join" test new "noop" engine command

* "noop" command is needed in this test to have a deterministic behavior
  regarding the last task in the workflow. Previously, there was a
  uncertainty wether task4 or task5 was going to run last and we couldn't
  reliably calculate workflow output. One more interesting thing: task5
  was added as a "no operation dead end" for task3 only. So it seemed to
  make perfect sense to avoid adding a whole task and just add a new
  no operation command instead.

Change-Id: Ie5d8861f289cb43bc383d0b617a95ae43185c86d
Merge "Working on "join": fixing "partial join" test new "noop" engine command"