update user merge function to work with new identifier model
update user merge function to work with new identifier model

DMPRoadmap/roadmap,CDLUC3/dmptool,DMPRoadmap/roadmap,DigitalCurationCentre/roadmap,DigitalCurationCentre/roadmap,DigitalCurationCentre/roadmap,CDLUC3/dmptool,DMPRoadmap/roadmap,CDLUC3/dmptool,CDLUC3/dmptool