Use ``hadoop fs -stat`` to check file existence.

def exists(self, path):
        """
        Use ``hadoop fs -stat`` to check file existence.
        """

        cmd = load_hadoop_cmd() + ['fs', '-stat', path]
        logger.debug('Running file existence check: %s', subprocess.list2cmdline(cmd))
        p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True, universal_newlines=True)
        stdout, stderr = p.communicate()
        if p.returncode == 0:
            return True
        else:
            not_found_pattern = "^.*No such file or directory$"
            not_found_re = re.compile(not_found_pattern)
            for line in stderr.split('\n'):
                if not_found_re.match(line):
                    return False
            raise hdfs_error.HDFSCliError(cmd, p.returncode, stdout, stderr)