When using the start process instance at activities feature implemented in CAM-3454, the variables submitted have no activity instance IDs.

This is ok if...
... we value the semantics of "startBefore"; start before means starting in a transition; an execution in a transition has no activity instance ID, thus the variables have no activity instance ID (this is also how process instance modification behaves at the moment)

This is not ok if..
... we need this to be consistent with the other startProcessInstance commands where the variables always have activity instance IDs (since firing history events is delayed until the initial activity has been entered)