action-fail: a jujuc command for Actions to set an error state

action-fail permits an Action to set an error value which will be returned to
the stateserver upon completion of the Action.  This does not prevent
action-set from adding more values to the results map.
I think you also want a `<-time.After(testing.ShortWait)` to continue to the top of the loop and trigger another StartSync -- you really can't depend on timing with the uniter tests