Patch script to retrieve all existing parent transformations

The change in the script (dirac-bookkeeping-prod4path.py) allows the retrieval of all parent Transformation IDs corresponding to given production identified by the BK query. This is useful for productions with more than 2 steps in case the user needs to find the ID of the MC*Simulation step. In previous version of the script this was not displayed. The implementation relies on the fact that the API call to get the parent always returns a long unless no other parent is available in which case one gets None as result.