Registry v1.0.3 adds support for ordering of Provisioning Targets. The easiest way to set this order for existing deployments is via Configuration >> Provisioning Targets >> Reorder Provisioning Targets. Drag the entries into the desired order. (If they are already in the desired order, you must drag at least one out of order, click Done, and then move it back to the desired order.)
If no order is specified, provisioners will continue to execute non-deterministically (the behavior prior to v1.0.3).