[JobRerunner] fix to also support jobs with dictionaries as parameters

As we found out, some jobs get a dictionary as parameter, and not just
an OpenStack ID as the code and comments suggest.

That makes things a bit complicated, as we still want to prevent jobs
running on the same id with the same callbacks from running, but need
to store the payload of the request (the dict) now as well for
re-execution.

Author: mutax