setup observations from the MODFLOW list file for
        volume and flux water buget information

def setup_water_budget_obs(self):
        """ setup observations from the MODFLOW list file for
        volume and flux water buget information

        """
        if self.mflist_waterbudget:
            org_listfile = os.path.join(self.org_model_ws,self.m.lst.file_name[0])
            if os.path.exists(org_listfile):
                shutil.copy2(org_listfile,os.path.join(self.m.model_ws,
                                                       self.m.lst.file_name[0]))
            else:
                self.logger.warn("can't find existing list file:{0}...skipping".
                                   format(org_listfile))
                return
            list_file = os.path.join(self.m.model_ws,self.m.lst.file_name[0])
            flx_file = os.path.join(self.m.model_ws,"flux.dat")
            vol_file = os.path.join(self.m.model_ws,"vol.dat")
            df = pyemu.gw_utils.setup_mflist_budget_obs(list_file,
                                                                flx_filename=flx_file,
                                                                vol_filename=vol_file,
                                                                start_datetime=self.m.start_datetime)
            if df is not None:
                self.obs_dfs["wb"] = df
            #line = "try:\n    os.remove('{0}')\nexcept:\n    pass".format(os.path.split(list_file)[-1])
            #self.logger.statement("forward_run line:{0}".format(line))
            #self.frun_pre_lines.append(line)
            self.tmp_files.append(os.path.split(list_file)[-1])
            line = "pyemu.gw_utils.apply_mflist_budget_obs('{0}',flx_filename='{1}',vol_filename='{2}',start_datetime='{3}')".\
                    format(os.path.split(list_file)[-1],
                           os.path.split(flx_file)[-1],
                           os.path.split(vol_file)[-1],
                           self.m.start_datetime)
            self.logger.statement("forward_run line:{0}".format(line))
            self.frun_post_lines.append(line)