Return a subset of hdrgo2usrgos.

def get_hdrgo2usrgos(self, hdrgos):
        """Return a subset of hdrgo2usrgos."""
        get_usrgos = self.hdrgo2usrgos.get
        hdrgos_actual = self.get_hdrgos().intersection(hdrgos)
        return {h:get_usrgos(h) for h in hdrgos_actual}