Get GoSubDag with paths from usrgos through hdrgo.

def _get_pltdag_path_hdr(self, hdrgo, usrgos, desc="pruned"):
        """Get GoSubDag with paths from usrgos through hdrgo."""
        go_sources = usrgos.union([hdrgo])
        gosubdag = GoSubDag(go_sources,
                            self.gosubdag.get_go2obj(go_sources),
                            relationships=self.gosubdag.relationships,
                            rcntobj=self.gosubdag.rcntobj,
                            go2nt=self.gosubdag.go2nt,
                            dst_srcs_list=[(hdrgo, usrgos), (None, set([hdrgo]))])
        tot_usrgos = len(set(gosubdag.go2obj.keys()).intersection(self.usrgos))
        return self.ntpltgo(
            hdrgo=hdrgo,
            gosubdag=gosubdag,
            tot_usrgos=tot_usrgos,
            parentcnt=True,
            desc=desc)