Performs an os.walk on a local or SSH filepath.

def walk(self, dirpath):
        """Performs an os.walk on a local or SSH filepath."""
        if self.is_ssh(dirpath):
            self._check_ftp()
            remotepath = self._get_remote(dirpath)
            return self._sftp_walk(remotepath)
        else:
            return os.walk(dirpath)