Dowload repodata.

def _download_repodata(self, checked_repos):
        """Dowload repodata."""
        self._files_downloaded = []
        self._repodata_files = []
        self.__counter = -1

        if checked_repos:
            for repo in checked_repos:
                path = self._repo_url_to_path(repo)
                self._files_downloaded.append(path)
                self._repodata_files.append(path)
                worker = self.download_async(repo, path)
                worker.url = repo
                worker.path = path
                worker.sig_finished.connect(self._repodata_downloaded)
        else:
            # Empty, maybe there is no internet connection
            # Load information from conda-meta and save that file
            path = self._get_repodata_from_meta()
            self._repodata_files = [path]
            self._repodata_downloaded()