private: set the omitted_parcov attribute

def __load_omitted_parcov(self):
        """private: set the omitted_parcov attribute
        """
        if self.omitted_parcov_arg is None and self.omitted_par_arg is None:
            raise Exception("ErrVar.__load_omitted_parcov: " +
                            "both omitted args are None")
        # try to set omitted_parcov by extracting from base parcov
        if self.omitted_parcov_arg is None and self.omitted_par_arg is not None:
            # check to see if omitted par names are in parcov
            found = True
            for par_name in self.omitted_jco.col_names:
                if par_name not in self.parcov.col_names:
                    found = False
                    break
            if found:
                # need to access attribute directly, not view of attribute
                self.__omitted_parcov = \
                    self._LinearAnalysis__parcov.extract(
                        row_names=self.omitted_jco.col_names)
            else:
                self.logger.warn("ErrVar.__load_omitted_parun: " +
                                 "no omitted parcov arg passed: " +
                        "setting omitted parcov as identity Matrix")
                self.__omitted_parcov = Cov(
                    x=np.ones(self.omitted_jco.shape[1]),
                    names=self.omitted_jco.col_names, isdiagonal=True)
        elif self.omitted_parcov_arg is not None:
            raise NotImplementedError()