workflows: passed data check

* Adds a check that passed data to the workflows API is indeed
  a list.

Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
workflows: wrong default position

* Fixes the default position of workflows when restarting a
  workflow.  (closes #2177) (PR #2186)

Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>